INTRODUCTION
[0001] Biomarkers (also called disease signatures) are specific analytes like RNA, DNA and
proteins that can be used as surrogates for a mechanism of action, disease state or
clinical endpoint. In particular, multiplexed or multimarker approaches may be used
in molecular diagnostics and personalized medicine, whose goal is to identify the
right treatment for the right patient at the right time and dose, or to detect early
complex diseases such as cancer and cardiovascular diseases sensitively and specifically.
DNA and protein microarrays have been developed to accommodate a large number of biomarkers.
[0002] Certain biomolecules, for example cancer embryonic antigen (CEA), could potentially
serve as a diagnostic indicator for early stage cancer. However, many of the proteins
which are expected to have diagnostic value are present in the bloodstream at extremely
low concentrations, which makes them challenging to quantify with analytical techniques.
[0003] Most commercial DNA microarray systems utilize fluorescent labeling (tagging) to
quantify biomolecular analytes (targets). They may be of limited sensitivity because
they require approximately 10
4 or more molecules to achieve a useful signal-to-noise ratio and are marginally quantitative
because of the optical systems involved, and also because of crosstalk and bleaching.
The optical detection systems are usually used in conjunction with amplification techniques
such as polymerase chain reaction (PCR) which multiplies the original biomolecules
by many orders of magnitude. Alternative microarray technologies with a higher sensitivity
may be useful in the field of molecular diagnostics and genomics.
[0004] US 2014/0266186 refers to magnetic sensors, which include a magnetic tunnel junction (MTJ) magnetoresistive
element, a first electrode contacting at least a portion of a surface of the MTJ magnetoresistive
element and extending beyond an edge of the surface of the MTJ magnetoresistive element,
and a second electrode contacting at least a portion of an opposing surface of the
MTJ magnetoresistive element and extending beyond an edge of the opposing surface
of the MTJ magnetoresistive element, where facing surfaces of the extending portions
of the first and second electrodes are non-overlapping.
[0005] WO 2013/155290 refers to a magnetic assay where capture probes are disposed on the sensor array
as capture probe spots that overlap with the sensor elements. The capture probes on
the sensor elements can be the same or they can be different. Two or more sample solutions
are also disposed on the sensor array as sample spots that overlap with the sensor
elements. Targets in the sample solutions can bind to the capture probes to provide
immobilized targets. Magnetically labeled probes capable of binding to targets are
provided to the assay, and the resulting assay signal is from immobilized magnetically
labeled probes at the sensor elements.
[0006] US 2005/0106758 refers to a biosensor not requiring washing of an unbonded label molecular by analyzing
an object to be measured such as an antigen, an antibody, a DNA, and an RNA through
magnetic field sensing. The biosensor is small in size, low in price, and high in
sensing accuracy. Semiconductor Hall devices are arrayed two-dimensionally on the
bottoms of recesses in the surface of a sensor chip to which bonded is a magnetic
molecule with which a magnetic particle is labeled so as to sense the magnetic field
produced along the sensor surface of the sensor chip. The surface area of each semiconductor
Hall device is less than the maximum cross section of the magnetic molecule, and the
intervals of the arrayed semiconductor Hall devices are larger than the diameter of
the magnetic Hall molecule.
[0007] The abstract of
EDELSTEIN R L ET AL, "THE BARC BIOSENSOR APPLIED TO THE DETECTION OF BIOLOGICAL WARFARE
AGENTS", BIOSENSORS AND BIOELECTRONICS, ELSEVIER SCIENCE LTD. UK, AMSTERDAM, NL, (20000101),
vol. 14, no. 10/11, doi:10.1016/S0956-5663(99)00054-8, ISSN 0956-5663, pages 805 -
813, XP001069427 [X] 1-3,5,8-15 ∗ see Fig. 2, p. 807
∗ [Y] 4,6,7, reads: The Bead ARray Counter (BARC) is a multi-analyte that uses , magnetic
microbeads, and giant magnetoresistive (GMR) sensors to detect and identify agents.
The current prototype is a table-top instrument consisting of a microfabricated chip
(solid substrate) with an array of GMR sensors, a chip carrier board with electronics
for lock-in detection, a fluidics cell and cartridge, and an
electromagnet.
DNA probes are patterned onto the solid substrate chip directly above the GMR sensors, and sample
analyte containing complementary DNA hybridizes with the probes on the surface. Labeled,
micron-sized magnetic beads are then injected that specifically bind to the sample
DNA. A magnetic field is applied, removing any beads that are not specifically bound
to the surface. The beads remaining on the surface are detected by the GMR sensors,
and the intensity and location of the signal indicate the concentration and identity
of present in the sample. The current BARC chip contains a 64-element sensor array,
however, with recent advances in magnetoresistive technology, chips with millions
of these GMR sensors will soon be commercially available, allowing
simultaneous detection of thousands of analytes. Because each GMR sensor is capable of detecting a single
magnetic bead, in theory, the BARC biosensor should be able to detect the presence
of a single analyte molecule.
SUMMARY
[0008] Provided are magnetic sensors, which include a magnetic sensor element having a sensor
surface modification and an inter-element area adjacent to the magnetic sensor element
and having an inter-element area surface modification comprising an analyte-specific
probe that specifically binds to a magnetically labelled analyte, where the sensor
surface modification and the inter-element area surface modification provide a binding
surface in the inter-element area. Also provided are devices, systems and methods
in which the subject magnetic sensors find use.
[0009] In some embodiments, the sensor surface modification and the inter-element area surface
modification include different surface modifications.
[0010] In some embodiments, the sensor surface modification and the inter-element area surface
modification include different chemical compositions.
[0011] In some embodiments, the sensor surface modification includes a layer of a metal
on a surface of the magnetic sensor element and the inter-element area surface modification
includes a layer of a dielectric material on a surface of the inter-element area.
In some embodiments, the metal is gold and the dielectric material is silicon dioxide.
[0012] In some embodiments, the sensor surface modification includes a layer of a dielectric
material on a surface of the magnetic sensor element and the inter-element area surface
modification includes a layer of a metal on a surface of the inter-element area. In
some embodiments, the dielectric material is silicon dioxide and the metal is gold.
[0013] In some embodiments, the inter-element area includes a side surface of the magnetic
sensor element having a side surface modification.
[0014] In some embodiments, the side surface modification is different from the sensor surface
modification.
[0015] In some embodiments, the side surface modification is different from the inter-element
area surface modification.
[0016] In some embodiments, the side surface modification is the same as the inter-element
area surface modification.
[0017] In some embodiments, the side surface modification has a thickness of 15 nm to 150
nm.
[0018] In some embodiments, the sensor surface modification and the inter-element area surface
modification each include a layer of a dielectric material and the side surface modification
of the magnetic sensor element includes a layer of a metal. In some embodiments, the
dielectric material is silicon dioxide and the metal is gold.
[0019] In some embodiments, the sensor surface modification includes a cover on a surface
of the magnetic sensor element.
[0020] In some embodiments, a width of the inter-element area is 0.5 times or more a width
of the magnetic sensor element.
[0021] In some embodiments, a length of the magnetic sensor element is 1.5 times or more
a width of the magnetic sensor element.
[0022] In some embodiments, the inter-element area has a depth of 25 nm or more.
[0023] In some embodiments, the magnetic sensor element includes a reference layer with
a magnetization substantially parallel to a width of the magnetic sensor element.
[0024] Aspects of the present disclosure include a magnetic sensor system that includes
a magnetic sensor device and a magnetic field source. The magnetic sensor device includes
a magnetic sensor array having two or more magnetic sensors each including a magnetic
sensor element having a sensor surface modification and an inter-element area adjacent
to the magnetic sensor element and having an inter-element area surface modification,
where the sensor surface modification and the inter-element area surface modification
provide a binding surface in the inter-element area.
[0025] In some embodiments, the magnetic sensor system includes a processor configured to
obtain an analyte-specific signal from the magnetic sensor device.
[0026] Aspects of the present disclosure include a method of evaluating whether an analyte
is present in a sample. The method includes contacting a magnetic sensor with a sample
to generate a signal and evaluating whether the analyte is present in the sample based
on the signal. The magnetic sensor includes a magnetic sensor element having a sensor
surface modification and an inter-element area adjacent to the magnetic sensor element
and having an inter-element area surface modification, where the sensor surface modification
and the inter-element area surface modification provide a binding surface in the inter-element
area.
[0027] In some embodiments, the method includes magnetically labeling the sample prior to
the contacting.
[0028] In some embodiments, the evaluating includes obtaining a signal from the magnetic
sensor as the magnetically-labeled sample contacts the magnetic sensor.
[0029] In some embodiments, the contacting includes applying a magnetic label to the magnetic
sensor after contacting the magnetic sensor with the sample.
[0030] Aspects of the present disclosure include a kit that includes a magnetic sensor device
and a magnetic label. The magnetic sensor device includes a magnetic sensor array
having two or more magnetic sensors each including a magnetic sensor element having
a sensor surface modification and an inter-element area adjacent to the magnetic sensor
element and having an inter-element area surface modification, where the sensor surface
modification and the inter-element area surface modification provide a binding surface
in the inter-element area.
BRIEF DESCRIPTION OF THE FIGURES
[0031]
FIG. 1 shows a cross-sectional drawing of a magnetic sensor according to embodiments
of the present disclosure.
FIG. 2 shows an image of an array of 80 magnetic sensors according to embodiments
of the present disclosure.
FIG. 3 shows an image of an enlargement of a magnetic sensor of FIG. 2, which shows
a plurality of magnetic sensor elements arranged in series and in parallel according
to embodiments of the present disclosure.
FIG. 4 shows an SEM image of an enlargement of an arrangement of magnetic sensor elements
and inter-element areas according to embodiments of the present disclosure.
DETAILED DESCRIPTION
[0032] Provided are magnetic sensors, which include a magnetic sensor element having a sensor
surface modification and an inter-element area adjacent to the magnetic sensor element
and having an inter-element area surface modification, where the sensor surface modification
and the inter-element area surface modification provide a binding surface in the inter-element
area. Also provided are devices, systems and methods in which the subject magnetic
sensors find use.
[0033] Before the present invention is described in greater detail, it is to be understood
that the scope of the present invention will be limited only by the appended claims.
Embodiments of the disclosure falling outside the scope of the claims are described
for illustrative purposes.
[0034] Where a range of values is provided, it is understood that each intervening value,
to the tenth of the unit of the lower limit unless the context clearly dictates otherwise,
between the upper and lower limit of that range and any other stated or intervening
value in that stated range, is encompassed within the disclosure. The upper and lower
limits of these smaller ranges may independently be included in the smaller ranges
and are also encompassed within the disclosure, subject to any specifically excluded
limit in the stated range. Where the stated range includes one or both of the limits,
ranges excluding either or both of those included limits are also included in the
disclosure.
[0035] Certain ranges are presented herein with numerical values being preceded by the term
"about." The term "about" is used herein to provide literal support for the exact
number that it precedes, as well as a number that is near to or approximately the
number that the term precedes. In determining whether a number is near to or approximately
a specifically recited number, the near or approximating unrecited number may be a
number which, in the context in which it is presented, provides the substantial equivalent
of the specifically recited number.
[0036] Unless defined otherwise, all technical and scientific terms used herein have the
same meaning as commonly understood by one of ordinary skill in the art to which this
invention belongs. Although any methods and materials similar or equivalent to those
described herein can also be used in the practice or testing of the present invention,
representative illustrative methods and materials are now described.
[0037] It is noted that, as used herein and in the appended claims, the singular forms "a",
"an", and "the" include plural referents unless the context clearly dictates otherwise.
It is further noted that the claims may be drafted to exclude any optional element.
As such, this statement is intended to serve as antecedent basis for use of such exclusive
terminology as "solely," "only" and the like in connection with the recitation of
claim elements, or use of a "negative" limitation.
[0038] In the following sections, the subject magnetic sensors are described first in greater
detail, followed by a description of the magnetic sensor devices, systems and methods
in which the subject magnetic sensors find use.
MAGNETIC SENSORS
[0039] Aspects of the present disclosure include a magnetic sensor. In some instances, the
magnetic sensor is configured to increase sensitivity of the magnetic sensor. For
example, the magnetic sensor may be configured to preferentially bind magnetic labels
on certain areas of the surface of the magnetic sensor to increase sensitivity of
the magnetic sensor to the bound magnetic labels. Increasing the sensitivity of the
magnetic sensor may facilitate an increase in the accuracy of the magnetic sensor,
and may facilitate the detection of specific analytes in a sample that may be present
in the sample at a low concentration.
[0040] In certain embodiments, the magnetic sensor includes a magnetic sensor element having
a sensor surface modification and an inter-element area adjacent to the magnetic sensor
element and having an inter-element area surface modification, where the sensor surface
modification and the inter-element area surface modification provide a binding surface
(e.g., magnetic label binding surface) in the inter-element area.
[0041] In certain embodiments, the magnetic sensor includes a magnetic sensor element. The
magnetic sensor element may be a giant magnetoresistive (GMR) element or a tunneling
magnetoresistive (TMR) element. For example, the magnetic sensor element may be a
spin valve magnetoresistive element or a magnetic tunnel junction (MTJ) magnetoresistive
element, each of which are described in additional detail in the sections below.
[0042] In certain embodiments, the magnetic sensor element includes a sensor surface modification.
The sensor surface modification may be configured to bind to a magnetic label. For
instance, the sensor surface modification may be configured to preferentially bind
to a magnetic label in a sample being analyzed by the magnetic sensor device. In certain
embodiments (and as described in additional detail herein), the sensor surface modification
may include an analyte-specific probe (e.g., a surface capture ligand) that specifically
binds to a magnetically labeled analyte, thereby indirectly binding a specific analyte
to the sensor surface.
[0043] In other embodiments, the sensor surface modification may be configured to minimize
binding of a magnetic label to the magnetic sensor element. For example, the sensor
surface modification may provide a surface on the magnetic sensor element that minimizes
binding interactions between the sensor surface and magnetic labels. In certain embodiments,
the sensor surface modification may not include an analyte-specific probe (e.g., a
surface capture ligand). Stated another way, the sensor surface may be substantially
free of an analyte-specific probe (e.g., a surface capture ligand).
[0044] In certain embodiments, the sensor surface modification includes a chemical modification.
In some instances, the sensor surface modification includes a layer of a metal. For
example, the metal may be gold. In some instances, the metal surface (e.g., gold surface)
may be modified to bind to a magnetic label. For example, the metal surface (e.g.,
gold surface) may be configured to preferentially bind to a magnetic label in a sample
being analyzed by the magnetic sensor device. In certain embodiments (and as described
in additional detail herein), the metal surface modification may include an analyte-specific
probe (e.g., a surface capture ligand) that specifically binds to a magnetically labeled
analyte, thereby indirectly binding a specific analyte to the metal sensor surface
modification.
[0045] In other embodiments, the metal surface (e.g., gold surface) may be configured to
minimize binding of a magnetic label to the magnetic sensor element. For example,
the metal surface (e.g., gold surface) may provide a surface on the magnetic sensor
element that minimizes binding interactions between the sensor surface and magnetic
labels. In certain embodiments, the metal sensor surface modification may not include
an analyte-specific probe (e.g., a surface capture ligand). Stated another way, the
metal sensor surface may be substantially free of an analyte-specific probe (e.g.,
a surface capture ligand).
[0046] As described above, the sensor surface modification may include a chemical modification.
In some instances, the sensor surface modification includes a layer of a dielectric
material. For example, the dielectric material may be silicon dioxide. In some instances,
the surface of the dielectric material may be modified to bind to a magnetic label.
For example, the surface of the dielectric material may be configured to preferentially
bind to a magnetic label in a sample being analyzed by the magnetic sensor device.
In certain embodiments (and as described in additional detail herein), the dielectric
surface modification may include an analyte-specific probe (e.g., a surface capture
ligand) that specifically binds to a magnetically labeled analyte, thereby indirectly
binding a specific analyte to the dielectric sensor surface modification.
[0047] In other embodiments, the surface of the dielectric material may be configured to
minimize binding of a magnetic label to the magnetic sensor element. For example,
the surface of the dielectric material may provide a surface on the magnetic sensor
element that minimizes binding interactions between the sensor surface and magnetic
labels. In certain embodiments, the dielectric sensor surface modification may not
include an analyte-specific probe (e.g., a surface capture ligand). Stated another
way, the dielectric sensor surface may be substantially free of an analyte-specific
probe (e.g., a surface capture ligand).
[0048] In some embodiments, the sensor surface modification includes a layer of the sensor
surface modification disposed on a surface of the magnetic sensor element. The layer
of the sensor surface modification may be a substantially contiguous surface layer.
By "contiguous" is meant that the sensor surface modification covers an area without
significant voids or discontinuous areas in the layer of the sensor surface modification.
[0049] In some cases, the layer of the sensor surface modification may be substantially
uniform in thickness. For example, the sensor surface modification may have a thickness
ranging from 1 nm to 1000 nm, such as from 5 nm to 750 nm, or 5 nm to 500 nm, or 10
nm to 250 nm, or 10 nm to 200 nm, or 10 nm to 150 nm, or 15 nm to 150 nm, or 15 nm
to 100 nm, or 15 nm to 75 nm, or 15 nm to 50 nm. In some cases, the sensor surface
modification has a thickness of 15 nm to 150 nm.
[0050] In certain embodiments, the magnetic sensor includes an inter-element area adjacent
to the magnetic sensor element. The inter-element area may be adjacent to the magnetic
sensor element such that one side of the inter-element area is in contact with one
side of the magnetic sensor element. For example, a length of an inter-element area
may be adjacent to (e.g., in contact with) a length of a magnetic sensor element.
In some cases, the inter-element area is adjacent to two magnetic sensor elements.
For instance, the inter-element area may be in between two magnetic sensor elements.
In some cases, the inter-element area is adjacent to a magnetic sensor element on
one side of the inter-element area and adjacent to another magnetic sensor element
on an opposing side of the inter-element area. For example, the inter-element area
may be coplanar with the adjacent magnetic sensor elements. In these embodiments,
the magnetic sensors and adjacent inter-element areas may be arranged in series. In
some cases, a plurality of magnetic sensor elements and a plurality of inter-element
areas may be arranged in series in an alternating pattern of magnetic sensor elements
and inter-element areas. As described above, each magnetic sensor element may be adjacent
to one or two inter-element areas on opposing sides of the magnetic sensor element,
and each inter-element area may be adjacent to one or two magnetic sensor elements
on opposing sides of the inter-element areas.
[0051] In certain embodiments, the inter-element area includes an inter-element area surface
modification. The inter-element area surface modification may be configured to bind
to a magnetic label. For instance, the inter-element area surface modification may
be configured to preferentially bind to a magnetic label in a sample being analyzed
by the magnetic sensor device. In certain embodiments (and as described in additional
detail herein), the inter-element area surface modification may include an analyte-specific
probe (e.g., a surface capture ligand) that specifically binds to a magnetically labeled
analyte, thereby indirectly binding a specific analyte to the surface of the inter-element
area.
[0052] In other embodiments, the inter-element area surface modification may be configured
to minimize binding of a magnetic label to the inter-element area. For example, the
inter-element area surface modification may provide a surface on the inter-element
area that minimizes binding interactions between the surface of the inter-element
area and magnetic labels. In certain embodiments, the inter-element area surface modification
may not include an analyte-specific probe (e.g., a surface capture ligand). Stated
another way, the inter-element area surface may be substantially free of an analyte-specific
probe (e.g., a surface capture ligand).
[0053] In certain embodiments, the inter-element area surface modification includes a chemical
modification. In some instances, the inter-element area surface modification includes
a layer of a metal. For example, the metal may be gold. In some instances, the metal
surface (e.g., gold surface) may be modified to bind to a magnetic label. For example,
the metal surface (e.g., gold surface) may be configured to preferentially bind to
a magnetic label in a sample being analyzed by the magnetic sensor device. In certain
embodiments (and as described in additional detail herein), the metal inter-element
area surface modification may include an analyte-specific probe (e.g., a surface capture
ligand) that specifically binds to a magnetically labeled analyte, thereby indirectly
binding a specific analyte to the metal inter-element area surface modification.
[0054] In other embodiments, the metal surface (e.g., gold surface) may be configured to
minimize binding of a magnetic label to the inter-element area. For example, the metal
surface (e.g., gold surface) may provide a surface on the inter-element area that
minimizes binding interactions between the surface of the inter-element area and magnetic
labels. In certain embodiments, the metal inter-element area surface modification
may not include an analyte-specific probe (e.g., a surface capture ligand). Stated
another way, the metal inter-element area surface may be substantially free of an
analyte-specific probe (e.g., a surface capture ligand).
[0055] As described above, the inter-element area surface modification may include a chemical
modification. In certain embodiments, the inter-element area surface modification
includes a layer of a dielectric material. For example, the dielectric material may
be silicon dioxide. In some instances, the surface of the dielectric material may
be modified to bind to a magnetic label. For example, the surface of the dielectric
material may be configured to preferentially bind to a magnetic label in a sample
being analyzed by the magnetic sensor device. In certain embodiments (and as described
in additional detail herein), the dielectric inter-element area surface modification
may include an analyte-specific probe (e.g., a surface capture ligand) that specifically
binds to a magnetically labeled analyte, thereby indirectly binding a specific analyte
to the dielectric inter-element area surface modification.
[0056] In other embodiments, the surface of the dielectric material may be configured to
minimize binding of a magnetic label to the inter-element area. For example, the surface
of the dielectric material may provide a surface on the inter-element area that minimizes
binding interactions between the surface of the inter-element area and magnetic labels.
In certain embodiments, the dielectric inter-element area surface modification may
not include an analyte-specific probe (e.g., a surface capture ligand). Stated another
way, the dielectric inter-element area surface may be substantially free of an analyte-specific
probe (e.g., a surface capture ligand).
[0057] In some embodiments, the inter-element area surface modification includes a layer
of the inter-element area surface modification disposed on a surface of the inter-element
area. The layer of the inter-element area surface modification may be a substantially
contiguous surface layer. By "contiguous" is meant that the inter-element area surface
modification covers an area without significant voids or discontinuous areas in the
layer of the inter-element area surface modification.
[0058] In some cases, the layer of the inter-element area surface modification may be substantially
uniform in thickness. For example, the inter-element area surface modification may
have a thickness ranging from 1 nm to 1000 nm, such as from 5 nm to 750 nm, or 5 nm
to 500 nm, or 10 nm to 250 nm, or 10 nm to 200 nm, or 10 nm to 150 nm, or 15 nm to
150 nm, or 15 nm to 100 nm, or 15 nm to 75 nm, or 15 nm to 50 nm. In some cases, the
inter-element area surface modification has a thickness of 15 nm to 150 nm.
[0059] In certain embodiments, the sensor surface modification and the inter-element area
surface modification include different surface modifications. In certain embodiments,
the sensor surface modification may be configured to minimize binding of a magnetic
label to the magnetic sensor element, and the inter-element area surface modification
may be configured to bind to a magnetic label as described herein (e.g., specific
binding to a magnetically labeled analyte through an analyte-specific probe (e.g.,
a surface capture ligand). In other embodiments, the sensor surface modification may
be configured to bind to a magnetic label as described herein (e.g., specific binding
to a magnetically labeled analyte through an analyte-specific probe (e.g., a surface
capture ligand), and the inter-element area surface modification may be configured
to minimize binding of a magnetic label to the magnetic sensor element.
[0060] As described above, in certain embodiments, the sensor surface modification and the
inter-element area surface modification include different surface modifications. In
some embodiments, the sensor surface modification and the inter-element area surface
modification include different chemical modifications (e.g., different chemical compositions).
For example, as described above, one surface modification may be a metal surface modification
and the other surface modification may be a dielectric layer surface modification.
In some embodiments, the sensor surface modification includes a layer of a metal on
a surface of the magnetic sensor element and the inter-element area surface modification
includes a layer of a dielectric material on a surface of the inter-element area.
In some cases, the metal is gold and the dielectric material is silicon dioxide. In
some embodiments, the sensor surface modification includes a layer of a dielectric
material on a surface of the magnetic sensor element and the inter-element area surface
modification includes a layer of a metal on a surface of the inter-element area. In
certain instances, the dielectric material is silicon dioxide and the metal is gold.
[0061] In certain embodiments, the sensor surface modification and the inter-element area
surface modification include the same (or substantially the same) surface modification.
In some embodiments, the sensor surface modification and the inter-element area surface
modification include the same (or substantially the same) chemical modifications (e.g.,
the same (or substantially the same) chemical compositions). For example, as described
above, the surface modifications may be metal surface modifications, or the surface
modifications may be dielectric layer surface modifications. In some embodiments,
the sensor surface modification and the inter-element area surface modification each
include a layer of a metal. In certain instances, the metal is gold. In other embodiments,
the sensor surface modification and the inter-element area surface modification each
include a layer of a dielectric material. In certain instances, the dielectric material
is silicon dioxide.
[0062] In certain embodiments, the inter-element area includes a surface modification on
a side surface of the magnetic sensor element. The side surface of the magnetic sensor
element may be a surface of the magnetic sensor element facing inter-element area,
such as facing an interior volume of the inter-element area. As such, the side surface
of the magnetic sensor element having a surface modification may be the side of the
magnetic sensor element that is adjacent to the inter-element area.
[0063] In some embodiments, the inter-element area includes a surface modification on a
side surface of the magnetic sensor element that is different from the sensor surface
modification and the inter-element area surface modification. In certain embodiments,
the sensor surface modification and the inter-element area surface modification may
be configured to minimize binding of a magnetic label to the magnetic sensor element,
and the side surface modification may be configured to bind to a magnetic label as
described herein (e.g., specific binding to a magnetically labeled analyte through
an analyte-specific probe (e.g., a surface capture ligand). In other embodiments,
the sensor surface modification and the inter-element area surface modification may
be configured to bind to a magnetic label as described herein (e.g., specific binding
to a magnetically labeled analyte through an analyte-specific probe (e.g., a surface
capture ligand), and the side surface modification may be configured to minimize binding
of a magnetic label to the magnetic sensor element.
[0064] As described herein, in some embodiments, the inter-element area includes a surface
modification on a side surface of the magnetic sensor element that is different from
the sensor surface modification and the inter-element area surface modification. In
some cases, the inter-element area includes a chemical modification (e.g., chemical
composition) on a side surface of the magnetic sensor element that is different from
the sensor surface chemical modification (e.g., chemical composition) and the inter-element
area surface chemical modification (e.g., chemical composition). For example, the
sensor surface modification and the inter-element area surface modification may each
include a layer of a metal and the side surface modification of the magnetic sensor
element may include a layer of a dielectric material. In some embodiments, the metal
is gold and the dielectric material is silicon dioxide. In other cases, the sensor
surface modification and the inter-element area surface modification may each include
a layer of a dielectric material and the side surface modification of the magnetic
sensor element may include a layer of a metal. In some embodiments, the dielectric
material is silicon dioxide and the metal is gold.
[0065] In certain embodiments, the inter-element area includes a surface modification on
a side surface of the magnetic sensor element that is the same as the inter-element
area surface modification and different from the sensor surface modification. In certain
embodiments, the sensor surface modification may be configured to minimize binding
of a magnetic label to the magnetic sensor element, and the side surface modification
and inter-element area surface modification may be configured to bind to a magnetic
label as described herein (e.g., specific binding to a magnetically labeled analyte
through an analyte-specific probe (e.g., a surface capture ligand). In other embodiments,
the sensor surface modification may be configured to bind to a magnetic label as described
herein (e.g., specific binding to a magnetically labeled analyte through an analyte-specific
probe (e.g., a surface capture ligand), and the side surface modification and the
inter-element area surface modification may be configured to minimize binding of a
magnetic label to the magnetic sensor element. For example, the inter-element area
may include a surface chemical modification (e.g., chemical composition) on a side
surface of the magnetic sensor element that is the same as the inter-element area
surface chemical modification (e.g., chemical composition) and different from the
sensor surface chemical modification (e.g., chemical composition).
[0066] In certain embodiments, as described above, the magnetic sensor element and the inter-element
area are substantially coplanar. In some cases, the side surface of the magnetic sensor
element forms an angle with the surface of the magnetic sensor element. For example,
the angle between the side surface of the magnetic sensor element and the surface
of the magnetic sensor element may be 90° or more, such as 95° or more, or 100° or
more, or 105° or more, or 110° or more, or 115° or more, or 120° or more. In certain
cases, the angle between the side surface of the magnetic sensor element and the surface
of the magnetic sensor element is 90°. In some cases, the side surface of the magnetic
sensor element forms a corresponding angle with the surface of the inter-element area.
For example, the angle between the side surface of the magnetic sensor element and
the surface of the inter-element area may be 90° or more, such as 95° or more, or
100° or more, or 105° or more, or 110° or more, or 115° or more, or 120° or more.
In certain cases, the angle between the side surface of the magnetic sensor element
and the surface of the inter-element area is 90°.
[0067] In certain embodiments, the side surface modification of the magnetic sensor element
has a thickness ranging from 1 nm to 1000 nm, such as from 5 nm to 750 nm, or 5 nm
to 500 nm, or 10 nm to 250 nm, or 10 nm to 200 nm, or 10 nm to 150 nm, or 15 nm to
150 nm, or 15 nm to 100 nm, or 15 nm to 75 nm, or 15 nm to 50 nm. In some cases, the
side surface modification of the magnetic sensor element has a thickness of 15 nm
to 150 nm.
[0068] In some embodiments, the sensor surface modification includes a cover on a surface
of the magnetic sensor element. For example the cover may be disposed on a surface
of the magnetic sensor element. In some instances, the cover is disposed over substantially
the entire surface of the magnetic sensor element (e.g., disposed over substantially
the entire top surface of the magnetic sensor element). The cover may be configured
to minimize and/or prevent magnetic label binding to a surface of the magnetic sensor
element. In these embodiments, a minimization of magnetic label binding to the surface
of the magnetic sensor element may facilitate an increase in the sensitivity of the
magnetic sensor to magnetic labels in the inter-element area. In some embodiments,
the cover is disposed over one or more magnetic sensor elements. For example, the
cover may be of a sufficient size to be disposed over two or more magnetic sensor
elements, or over an array of magnetic sensor elements. As described in more detail
below, the inter-element areas adjacent to the magnetic sensor elements may have a
surface (e.g., top surface) that is at a depth below the top surfaces of the adjacent
magnetic sensor elements. In these embodiments, the cover disposed on the surfaces
of the magnetic sensor elements forms a conduit in the inter-element areas. For instance,
the conduit may be bounded on the top by the cover, on the bottom by the inter-element
area, and on opposing sides by the side surfaces of magnetic sensor elements adjacent
to opposing sides of the inter-element area. In certain cases, a sample may be applied
to the magnetic sensor through the conduit and may thus contact the inter-element
area and side surfaces of the magnetic sensor elements.
[0069] In certain embodiments, a width of the inter-element area is less than a width of
the magnetic sensor element. For example, the width of the inter-element area may
be 0.1 times or more the width of the magnetic sensor element, such as 0.2 times or
more, or 0.3 times or more, or 0.4 times or more, or 0.5 times or more, or 0.6 times
or more, or 0.7 times or more, or 0.8 times or more, or 0.9 times or more the width
of the magnetic sensor element. In certain cases, the width of the inter-element area
is 0.5 times or more the width of the magnetic sensor element.
[0070] In certain embodiments, a length of the magnetic sensor element is greater than a
width of the magnetic sensor element. For example, the length of the magnetic sensor
element may be 1.1 times or more a width of the magnetic sensor element, such as 1.2
times or more, or 1.3 times or more, or 1.4 times or more, or 1.5 times or more, or
1.6 times or more, or 1.7 times or more, or 1.8 times or more, or 1.9 times or more,
or 2 times or more the width of the magnetic sensor element. In certain cases, the
length of the magnetic sensor element is 1.5 times or more a width of the magnetic
sensor element.
[0071] In certain embodiments, the inter-element area adjacent to the magnetic sensor element
may have a surface (e.g., top surface) that is at a depth below the top surface of
the adjacent magnetic sensor element. In these embodiments, the inter-element area
and the magnetic sensor element may be coplanar, e.g., the inter-element area and
the magnetic sensor element may be arranged on a common (planar) surface of a magnetic
sensor device support. In some cases, the top surface of the magnetic sensor element
may be at a distance above the surface of the magnetic sensor device support that
is greater than the distance above the surface the inter-element area extends. Stated
another way, the height of the inter-element area may be less than the height of an
adjacent magnetic sensor element. Thus, as measured from the top surface of the magnetic
sensor element, the inter-element area may have a depth below the top surface of the
magnetic sensor element of 5 nm or more, such as 10 nm or more, or 15 nm or more,
or 20 nm or more, or 25 nm or more, or 30 nm, or more, or 35 nm or more, or 40 nm
or more, or 45 nm or more, or 50 nm or more, or 55 nm or more, or 60 nm or more, or
65 nm or more, or 70 nm or more, or 75 nm or more, or 80 nm or more, or 85 nm or more,
or 90 nm or more, or 95 nm or more, or 100 nm or more. In certain cases, the inter-element
area has a depth below the top surface of the magnetic sensor element of 25 nm or
more.
[0072] In certain embodiments, the magnetic sensor element width and inter-element area
width is 10 µm or less, such as 9 µm or less, or 8 µm or less, or 7 µm or less, or
6 µm or less, or 5 µm or less, or 4 µm or less, or 3 µm or less, or 2 µm or less,
or 1 µm or less. In certain cases, the magnetic sensor element width and inter-element
area width is 2 µm or less.
[0073] In certain embodiments, the magnetic sensor element includes a reference layer with
a magnetization substantially parallel to a width of the magnetic sensor element.
For example, the width dimension of the magnetic sensor element may be disposed along
an axis, and the magnetic sensor element includes a reference layer with a magnetization
substantially parallel to the axis. By "substantially parallel" is meant that the
magnetization of the reference layer is aligned at 25° or less to the axis, such as
20° or less, or 15° or less, or 10°or less, or 5° or less, or 4° or less, or 3° or
less, or 2° or less, or 1 ° or less to the axis (e.g., to the width dimension of the
magnetic sensor element). In certain cases, the magnetization of the reference layer
is aligned at 10°or less to the axis (e.g., to the width dimension of the magnetic
sensor element).
[0074] FIG. 1 shows a cross-sectional drawing of a magnetic sensor according to embodiments
of the present disclosure. As shown in FIG. 1, a magnetic sensor includes a magnetic
sensor element, such as a giant magnetoresistive (GMR) element (also referred to herein
as a GMR film), on a support, such as a support composed of a dielectric material
(also referred to herein as a dielectric layer (DL), which may be composed of an oxide
such as silicon dioxide. The magnetic sensor element (GMR film) has a sensor width
(SW) and a sensor length (SL). The magnetic sensor element (GMR film) includes a sensor
surface modification (SSM) on a surface of the magnetic sensor element. Adjacent to
the magnetic sensor element along the sensor length (SL) is an inter-element area
(also referred to herein as a trench). The inter-element area (trench) has an inter-element
area width (trench width (TW)) and an inter-element area depth (trench depth (TD)).
The inter-element area has an inter-element area length (trench length) that is substantially
the same as the sensor length (SL). The inter-element area is adjacent to the magnetic
sensor element along the side (also referred to herein as the sensor edge (SE)) of
the magnetic sensor element. The side of the magnetic sensor element (sensor edge
(SE)) may have a side surface modification as described herein, such as a layer of
a dielectric material (or a metal). The side surface modification has a thickness
(TH). The inter-element area includes an inter-element area surface modification as
described herein (also referred to herein as a trench surface modification (TSM)).
As shown in FIG. 1, more than one magnetic sensor may be arranged in series to form
an array of magnetic sensors.
[0075] FIG. 4 shows an SEM image of an enlargement of an arrangement of magnetic sensor
elements and inter-element areas according to embodiments of the present disclosure.
MAGNETIC SENSOR DEVICES
[0076] Aspects of the present disclosure include magnetic sensor devices. The magnetic sensor
device includes a support. In some embodiments, the support includes an array of magnetic
sensors (e.g., an array of biosensors) disposed thereon. In certain embodiments, each
magnetic sensor includes one or more magnetic sensor elements as described herein,
and one or more inter-element areas as described herein. Aspects of the magnetic sensors
are described further in the following sections.
[0077] In certain embodiments, a magnetic sensor includes two or more magnetic sensor elements.
In some cases, the magnetic sensor elements are electrically connected to each other.
In certain cases, the magnetic sensor elements are electrically connected to each
other in series. For example, the magnetic sensor elements may be electrically connected
to each other in series by one or more electrodes. In some embodiments, by electrically
connecting the magnetic sensor elements together in series, a current (e.g., a sense
current) may flow through the magnetic sensor elements in series (e.g., sequentially).
[0078] In certain embodiments, an array of magnetic sensor elements includes a plurality
of magnetic sensor elements arranged in series and/or in parallel, which may include
two or more magnetic sensor elements, including 3 or more, 4 or more, 6 or more, 8
or more, 10 or more, 15 or more, 20 or more, 25 or more, 30 or more, 40 or more, 50
or more, 75 or more, 100 or more, 125 or more, 150 or more, 175 or more, 200 or more,
225 or more, or 250 or more magnetic sensors arranged in series and/or in parallel.
In some cases, the array of magnetic sensor elements includes 100 or more magnetic
sensor elements arranged in series and/or in parallel. FIG. 3 shows an enlargement
of a magnetic sensor of FIG. 2, which shows a plurality of magnetic sensor elements
arranged in series and in parallel according to embodiments of the present disclosure.
[0079] In some instances, the magnetic sensor elements are arranged (e.g., arranged in series
and/or in parallel as described above) such that the distance between adjacent magnetic
sensor elements is 50 µm or less, such as 40 µm or less, including 30 µm or less,
or 20 µm or less, or 10 µm or less, or 5 µm or less, or 4 µm or less, or 3 µm or less,
or 2 µm or less, or 1 µm or less. In some cases, the distance between adjacent magnetic
sensor elements is 2 µm.
[0080] In certain embodiments, a magnetic sensor element may have dimensions in the range
of 2 µm x 2 µm to 200 µm x 200 µm, including dimensions of 2 µm x 200 µm or less,
such as 100 µm x 2 µm or less, for instance 2 µm x 100 µm or less, or 100 µm x 100
µm or less, or 10 µm x 10 µm or less, or 5 µm x 5 µm or less, or 3 µm x 3 µm or less,
or 2 µm x 2 µm or less, or 1 µm x 1 µm or less.
[0081] In some instances, an inter-element area has dimensions in the range of 1 µm x 1
µm to 100 µm x 100 µm, including dimensions of 1 µm x 100 µm or less, such as 50 µm
x 1 µm or less, for instance 1 µm x 50 µm or less, or 50 µm x 50 µm or less, or 5
µm x 5 µm or less, or 4 µm x 4 µm or less, or 3 µm x 3 µm or less, or 2 µm x 2 µm
or less, or 1 µm x 1 µm or less.
[0082] In certain embodiments, an electrode is composed of an electrically conductive material.
In some cases, the electrode is made of a conductive metal, e.g., copper, aluminum,
palladium, a palladium alloy, a palladium oxide, platinum, a platinum alloy, a platinum
oxide, ruthenium, a ruthenium alloy, a ruthenium oxide, silver, a silver alloy, a
silver oxide, tin, a tin alloy, a tin oxide, titanium, a titanium alloy, a titanium
oxide, tantalum, a tantalum alloy, a tantalum oxide, combinations thereof, and the
like. In some instances, the electrode is made of tantalum. In some instances, the
electrode is made of ruthenium. In some instances, the electrode includes a layer
of an electrically conductive material as described above. For example, the electrode
may include a layer of a conductive metal, such as tantalum. In some instances, the
electrode includes two or more layers of electrically conductive materials as described
above. For example, the electrode may include alternating layers of two different
conductive metals, such as tantalum and ruthenium.
[0083] In certain embodiments, a magnetic sensor includes a plurality of magnetic sensor
elements. In some cases, the magnetic sensor includes two or more magnetic sensor
elements (e.g., two or more magnetic sensor elements arranged in series), as described
above. In some instances, the magnetic sensor device includes magnetic sensor elements
arranged in series and additional magnetic sensor elements electrically connected
in parallel to the first series of magnetic sensor arrays. The additional magnetic
sensor elements may include two or more magnetic sensor elements arranged in series
as described above. As such, in certain cases, the magnetic sensor may include an
arrangement of magnetic sensor elements where a plurality of magnetic sensor elements
are electrically connected both in series and in parallel.
[0084] Aspects of the present disclosure include a magnetic sensor device, where the magnetic
sensor device includes a support. In some embodiments, the support includes an array
of magnetic sensors (e.g., an array of biosensors) disposed thereon. In certain embodiments,
the support has a thickness of 5 mm or less, such as 2 mm or less, including 1.6 mm
or less, or 1.0 mm or less, or 0.5 mm or less, or 0.3 mm or less, or 0.2 mm or less.
In certain embodiments, the support has a width of 20 mm or less, or 15 mm or less,
such as 12 mm or less, including 10 mm or less, or 5 mm or less, or 2 mm or less.
[0085] In certain embodiments, the support of the magnetic sensor device is shaped as a
rectangular solid (although other shapes are possible), having a length ranging from
1 mm to 20 mm, such as 1 mm to 10 mm, including 1 mm to 5 mm; a width ranging from
1 mm to 20 mm, such as 1 mm to 10 mm, including 1 mm to 5 mm, or 1 mm to 3 mm; and
a thickness ranging from 0.1 mm to 5 mm, such as 0.2 mm to 1 mm, including 0.3 mm
to 0.5 mm.
Magnetic Sensor Arrays
[0086] In certain embodiments, the magnetic sensor device includes an array of magnetic
sensors (e.g., an array of biosensors). The array of magnetic sensors may have a variety
of different configurations, e.g., with respect to magnetic sensor configuration.
In certain embodiments, the subject magnetic sensors are arranged on a biochip (e.g.,
a biosensor chip). By "biochip" or "biosensor chip" is meant a magnetic sensor device
that includes an array of magnetic sensors (e.g., an array of biosensors). For instance,
a biochip may include a magnetic sensor device that includes a support surface which
displays two or more distinct arrays of magnetic sensors on the support surface. In
certain embodiments, the magnetic sensor device includes a support surface with an
array of magnetic sensors.
[0087] An "array" includes any two-dimensional or substantially two-dimensional (as well
as a three-dimensional) arrangement of addressable regions, e.g., spatially addressable
regions. An array is "addressable" when it has multiple sensors positioned at particular
predetermined locations (e.g., "addresses") on the array. Array features (e.g., sensors)
may be separated by intervening spaces. Any given support may carry one, two, four
or more arrays disposed on a front surface of the support. Depending upon the use,
any or all of the arrays may be the same or different from one another and each may
contain multiple distinct magnetic sensors. An array may contain one or more, including
2 or more, 4 or more, 8 or more, 10 or more, 50 or more, 100 or more, 250 or more,
500 or more, 750 or more, 1000 or more magnetic sensors. For example, 64 magnetic
sensors can be arranged into an 8×8 array, or 80 magnetic sensors can be arranged
in an 8x10 array, or 90 sensors can be arranged in a 9x10 array. FIG. 2 shows an image
of an array of 80 magnetic sensors according to embodiments of the present disclosure.
[0088] In some instances, the magnetic sensors are arranged in the array in rows and columns
of magnetic sensors. For example, an array may include one or more rows of two or
more magnetic sensors. In some cases, an array includes 1 or more rows, such as 2
or more, or 3 or more, or 4 or more, or 5 or more, or 6 or more, or 7 or more, or
8 or more, or 9 or more, or 10 or more, or 12 or more, or 14 or more, or 16 or more,
or 18 or more, or 20 or more, or 25 or more, or 30 or more, or 35 or more, or 40 or
more, or 45 or more, or 50 or more rows of magnetic sensors. In some cases, an array
includes 1 or more columns, such as 2 or more, or 3 or more, or 4 or more, or 5 or
more, or 6 or more, or 7 or more, or 8 or more, or 9 or more, or 10 or more, or 12
or more, or 14 or more, or 16 or more, or 18 or more, or 20 or more, or 25 or more,
or 30 or more, or 35 or more, or 40 or more, or 45 or more, or 50 or more columns
of magnetic sensors. For example, 64 magnetic sensors can be arranged into an 8×8
array that includes 8 rows and 8 columns of magnetic sensors, or 80 magnetic sensors
can be arranged in an 8x10 array that includes 10 rows and 8 columns of magnetic sensors.
[0089] In certain embodiments, the magnetic sensors can be arranged into an array with an
area of 10 cm
2 or less, or 9 cm
2 or less, 5 cm
2 or less, 4 cm
2 or less, e.g., 2 cm
2 or less, 1.2 cm
2 or less, 0.1 cm
2 or less, including 50 mm
2 or less, 20 mm
2 or less, such as 10 mm
2 or less, or even smaller. For example, the magnetic sensors can be arranged into
an array with an area of 15 mm
2 or less, such as 12.2 mm
2 or less (e.g., 3.2 mm x 3.8 mm). In some instances, the magnetic sensors are arranged
into an array with an area of 20 mm
2. For instance, the magnetic sensors may have a density in an array of 1 magnetic
sensor per 2 mm
2 array area or less, such as 1 magnetic sensor per 1 mm
2 array area or less, or 1 magnetic sensor per 0.5 mm
2 array area, or 1 magnetic sensor per 0.2 mm
2 array area, or 1 magnetic sensor per 0.16 mm
2 array area, or 1 magnetic sensor per 0.14 mm
2 array area, or 1 magnetic sensor per 0.12 mm
2 array area, or 1 magnetic sensor per 0.1 mm
2 array area, or 1 magnetic sensor per 0.08 mm
2 array area, or 1 magnetic sensor per 0.05 mm
2 array area. In some cases, the magnetic sensors may have a density in an array of
1 magnetic sensor per 0.16 mm
2 array area.
[0090] In some embodiments, magnetic biosensors with multiple magnetic sensor elements,
according to the embodiments of the present disclosure, are dimensioned to cover a
portion of the support which is contacted with a sample of biological molecules during
an assay. The placement of the sample (e.g., biological molecules) onto individual
sensors or inter-element areas may be performed by placing small droplets of a liquid
sample with biological molecules onto certain regions of the support, or by placing
a stamp coated with biological molecules into contact with the support. In some embodiments,
the area of the support coated by a sample of biological molecules and the area of
a biosensor are substantially similar. For example, the biosensor may have dimensions
in the range of 10 µm x 10 µm to 1000 µm x 1000 µm, including dimensions of 10 µm
x 1000 µm or less, such as 1000 µm x 10 µm or less, for instance 800 µm x 800 µm or
less, or 400 µm x 400 µm or less, or 200 µm x 200 µm or less, or 180 µm x 180 µm or
less, or 160 µm x 160 µm or less, or 140 µm x 140 µm or less, or 120 µm x 120 µm or
less, or 100 µm x 100 µm or less, or 80 µm x 80 µm or less, or 50 µm x 50 µm or less,
or 30 µm x 30 µm or less. In some instances, a biosensor has dimensions of 140 µm
x 140 µm or less, such as 120 µm x 120 µm.
[0091] In some embodiments, magnetic biosensors with multiple magnetic sensor elements,
according to the embodiments of the present disclosure, are spaced apart such that
the number of biosensors per unit area is maximized, while still allowing individual
biosensors to be contacted with separate droplets of a liquid sample containing biological
molecules. To achieve substantial separation between adjacent droplets of liquid placed
onto individual biosensors, the biosensors may be spaced a certain distance apart
and separated by the inter-element areas as described herein.
[0092] In certain embodiments, at least some, or all, of the magnetic sensors have an analyte-specific
probe (e.g., a surface capture ligand) stably associated with a surface of the sensor
or a surface or the inter-element area. For example, each magnetic sensor array may
include one or more magnetic sensors having an analyte-specific probe bound to a surface
of the magnetic sensor or the inter-element area. Where a given array includes two
or more magnetic sensors, each sensor or inter-element area may have the same or different
analyte-specific probe associated with its surface. For example, a magnetic sensor
array may include two or more distinct magnetic sensors or inter-element areas each
configured to specifically detect the same analyte. In some cases, different analyte-specific
probes may be present on the sensor surfaces or the inter-element area surfaces of
such devices, such that each different analyte-specific probe specifically binds to
a distinct analyte. For instance, a magnetic sensor array may include two or more
distinct magnetic sensors or distinct inter-element areas each configured to specifically
detect a different analyte. In other cases, the magnetic sensor devices include magnetic
sensors or inter-element areas that are free of any analyte-specific probes, such
that the surface of the magnetic sensor or inter-element area is functionalized to
bind directly to the analyte. In some instances, the magnetic sensor or inter-element
area includes a blocking layer disposed over the surface of the magnetic sensor or
inter-element area. The blocking layer may be configured to inhibit the binding of
any analyte-specific probes or analyte to the surface of the magnetic sensor (e.g.,
where such blocked magnetic sensors may serve as sources of reference or control electrical
signals) or inter-element area (e.g., where such blocked inter-element areas may serve
as sources of reference or control electrical signals).
[0093] As described above, in certain embodiments, the magnetic sensor device includes two
or more magnetic sensor arrays disposed on a support. As such, the magnetic sensor
device includes two or more magnetic sensor arrays. As described above, each magnetic
sensor array may have one or more magnetic sensors or inter-element areas with each
magnetic sensor or inter-element area configured to detect the same or different analytes.
Thus, each magnetic sensor array on the magnetic sensor device may be configured to
detect the same set or different sets of analytes. For example, a magnetic sensor
device may include two or more distinct magnetic sensor arrays each configured to
specifically detect the same set of analytes. In other cases, a magnetic sensor device
may include two or more distinct magnetic sensor arrays each configured to specifically
detect a different set of analytes.
[0094] Electronic communication elements, e.g., conductive leads, may be present which are
configured to electronically couple the magnetic sensors to components of the system,
such as processors, displays, etc. Additionally, a given magnetic sensor device may
include a variety of other components in addition to the magnetic sensor array. Additional
magnetic sensor device components may include, but are not limited to: signal processing
components, power sources, fluid handling components, wired or wireless communication
components, etc.
[0095] In certain embodiments, the magnetic sensor device is configured to produce a detectable
signal from a minimum amount of sample. In some instances, the magnetic sensor device
is configured to produce a detectable signal from a sample size of 10 mL or less,
or 5mL or less, or 3 mL or less, or 1 mL or less, such as 500 µL or less, including
100 µL or less, for example 50 µL or less, or 25 µL or less, or 10 µL or less. As
such, in some cases, the inter-element areas may be configured to receive a minimum
amount of sample needed to produce a detectable signal. For example, the inter-element
areas may be configured to receive a sample of 10 mL or less, or 5 mL or less, or
3 mL or less, or 1 mL or less, such as 500 µL or less, including 100 µL or less, for
example 50 µL or less, or 25 µL or less, or 10 µL or less, or 5 µL or less, or 1 µL
or less.
[0096] In some embodiments, the magnetic sensor device is configured to connect to a system
for detecting the presence of an analyte in a sample. Accordingly, in certain embodiments,
the magnetic sensor device does not include a magnetic field source. The magnetic
field source may be included in the system for detecting the presence of an analyte
in the sample and, thus not included in the magnetic sensor device itself. Thus, the
assay protocol may include operably coupling the magnetic sensor device to the system
for detecting the presence of an analyte in the sample. In some instances, the magnetic
sensor device may be operably coupled to an activation and signal processing unit
of the system, as described herein. The magnetic sensor device may include one or
more electrical contacts configured to electrically connect the magnetic sensor device
to the system, such as to the activation and signal processing unit of the system.
The electrical contacts may be arranged along an edge of the magnetic sensor device.
[0097] In certain embodiments, the magnetic sensor device includes a programmable memory.
In some cases, the programmable memory is configured to store information, such as
information including, but not limited to: calibration data (e.g., calibration data
for each magnetic sensor and/or each magnetic sensor array); a record of how the magnetic
sensors have been prepared with surface functionalization molecules prior to the assay;
a record of completed assay steps; a record about which sample was measured; a record
of the measurement results; and the like. In some instances, a barcode may be used
instead of, or in addition to, the programmable memory. In embodiments of the magnetic
sensor device that include a barcode, information associated with the magnetic sensor
device may be stored and retrieved from an information system separate from the magnetic
sensor device, such as the activation and signal processing unit of the system.
Magnetic Sensors
[0098] As described above, each magnetic sensor may include one or more magnetic sensor
elements. In some cases, magnetic sensors are sensors configured to detect the presence
of nearby magnetic labels without any direct physical contact between the magnetic
sensor and the magnetic label. In certain embodiments, the magnetic sensors are configured
to detect the presence of an analyte in a sample. For example, a magnetic label may
be bound, either directly or indirectly, to an analyte, which in turn may be bound,
either directly or indirectly, to the magnetic sensor. If the bound magnetic label
is positioned within the detection range of the magnetic sensor, then the magnetic
sensor may provide a signal indicating the presence of the bound magnetic label, and
thus indicating the presence of the analyte.
[0099] In some instances, the magnetic sensors have a detection range from 1 nm to 1000
nm from the surface of the magnetic sensor, such as from 1 nm to 800 nm, including
from 1 nm to 500 nm, such as from 1 nm to 300 nm, including from 1 nm to 100 nm from
the surface of the magnetic sensor. In some instances, a minimization of the detection
range of the sensors may facilitate detection of specifically bound analytes while
minimizing detectable signals from analytes not of interest. By "detection range"
is meant the distance from the surface of the magnetic sensor where the presence of
a magnetic label will induce a detectable signal in the magnetic sensor. In some cases,
magnetic labels positioned close enough to the surface of the magnetic sensor to be
within the detection range of the magnetic sensor will induce a detectable signal
in the magnetic sensor. In certain instances, magnetic labels positioned at a distance
from the surface of the magnetic sensor that is greater than the detection range of
the magnetic sensor will not induce a detectable or non-negligible signal in the magnetic
sensor. For example, a magnetic label may have a magnetic flux that is proportional
to 1/r
3, where r is the distance between the magnetic sensor and the magnetic label. Thus,
only those magnetic labels that are positioned in close proximity (e.g., within the
detection range of the magnetic sensor) will induce a detectable signal in the magnetic
sensor.
[0100] In certain embodiments, the surface of the magnetic sensor is functionalized to bind
directly to an analyte or a magnetic label. For example, the surface of the magnetic
sensor may be functionalized to provide for covalent binding or non-covalent association
between the analyte or the magnetic label and magnetic sensor, including, but not
limited to, non-specific adsorption, binding based on electrostatic interactions (e.g.,
ion-ion pair interactions), hydrophobic interactions, hydrogen bonding interactions,
and the like.
[0101] In some instances, the surface of the magnetic sensor or the inter-element area includes
an analyte-specific probe (e.g., a surface capture ligand) that specifically binds
to an analyte. The analyte-specific probe may be bound to the surface of the magnetic
sensor or the inter-element area. For instance, a cationic polymer such as polyethyleneimine
(PEI) can be used to nonspecifically bind charged antibodies to the surface via physiabsorption.
Alternatively, a covalent chemistry can be used utilizing free amines or free thiol
groups on the analyte-specific probe to covalently bind the analyte-specific probe
to the surface of the magnetic sensor or the inter-element area. For example, an N-hydroxysuccinimide
(NHS) to 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) coupling system may
be used to covalently bind the analyte-specific probe to the surface of the magnetic
sensor or the inter-element area.
[0102] The analyte-specific probe may include one member of a specific binding pair. For
example, suitable specific binding pairs include, but are not limited to: a member
of a receptor/ligand pair; a ligand-binding portion of a receptor; a member of an
antibody/antigen pair; an antigen-binding fragment of an antibody; a hapten; a member
of a lectin/carbohydrate pair; a member of an enzyme/substrate pair; biotin/avidin;
biotin/streptavidin; digoxin/antidigoxin; and the like. In certain embodiments, the
surface of the magnetic sensor or the inter-element area includes an antibody that
specifically binds to an analyte of interest. Accordingly, contacting the magnetic
sensor or the inter-element area with an assay composition that includes the analyte
of interest may result in binding of the analyte to the analyte-specific probe (e.g.,
antibody) bound to the surface of the magnetic sensor or the inter-element area.
[0103] In certain embodiments, the magnetic sensor is configured to generate an electrical
signal in response to a magnetic label in proximity to a surface of the magnetic sensor.
For example, the magnetic sensors may be configured to detect changes in the resistance
of the magnetic sensor induced by changes in the local magnetic field. In some cases,
binding of a magnetic label (e.g., a magnetic nanoparticle label) in close proximity
to the magnetic sensor, as described above, induces a detectable change in the resistance
of the magnetic sensor. For instance, in the presence of an applied external magnetic
field, the magnetic labels near the magnetic sensor may be magnetized. The local magnetic
field of the magnetized magnetic labels may induce a detectable change in the resistance
of the underlying magnetic sensor. Thus, the presence of the magnetic labels can be
detected by detecting changes in the resistance of the magnetic sensor. In certain
embodiments, the magnetic labels near the magnetic sensor may be present in an inter-element
area such as bound to an inter-element area as described herein. In certain embodiments,
the magnetic labels near the magnetic sensor may be present in an inter-element area
such as bound to a side surface of a magnetic sensor element as described herein.
[0104] In certain embodiments, the magnetic sensors are configured to detect changes in
resistance of 1 Ohm or less, such as 500 mOhm or less, including 100 mOhm or less,
or 50 mOhm or less, or 25 mOhm or less, or 10 mOhm or less, or 5 mOhm or less, or
1 mOhm or less. In certain embodiments, the change in resistance may be expressed
in parts per million (PPM) relative to the original sensor resistance, such as a change
in resistance of 2 PPM or more, or 20 PPM or more, or 200 PPM or more, or 400 PPM
or more, or 600 PPM or more, or 1000 PPM or more, or 2000 PPM or more, or 4000 PPM
or more, or 6000 PPM or more, or 10,000 PPM or more, or 20,000 PPM or more, or 40,000
PPM or more, or 60,000 PPM or more, or 100,000 PPM or more, or 200,000 PPM or more.
[0105] In certain cases, the magnetic sensor is a multilayer thin film structures. The sensors
may include alternating layers of a ferromagnetic material and a non-magnetic material.
The ferromagnetic material may include, but is not limited to, Permalloy (NiFe), iron
cobalt (FeCo), nickel iron cobalt (NiFeCo), nickel oxide (NiO), cobalt oxide (CoO),
nickel cobalt oxide (NiCoO), ferric oxide (Fe
2O
3), CoFeB, Ru, PtMn, combinations thereof, and the like. In some cases, the non-magnetic
material is an insulating layer, such as, but not limited to, MgO, alumina, and the
like. In certain embodiments, the ferromagnetic layers have a thickness of 1 nm to
10 nm, such as 2 nm to 8 nm, including 3 nm to 4 nm. In some instances, the non-magnetic
layer has a thickness of 0.2 nm to 5 nm, such as 1 nm to 3 nm, including 1.5 nm to
2.5 nm, or 1.8 nm to 2.2 nm.
Spin Valve Magnetoresistive Elements
[0106] In certain embodiments, the magnetic sensor element is a spin valve magnetoresistive
element. In certain cases, the spin valve element is a multilayer structure that includes
a first ferromagnetic layer, a non-magnetic layer disposed on the first ferromagnetic
layer, and a second ferromagnetic layer disposed on the non-magnetic layer. The first
ferromagnetic layer may be configured to have its magnetization vector fixed in a
certain direction. In some cases, the first ferromagnetic layer is called the "pinned
layer". In certain embodiments, the spin valve element includes a pinned layer with
a magnetization substantially parallel to a width of the magnetic sensor element,
as described above. The second ferromagnetic layer may be configured such that its
magnetization vector can rotate freely under an applied magnetic field. In some cases,
the second ferromagnetic layer is called the "free layer".
[0107] In certain instances, the electrical resistance of a spin valve element depends on
the relative orientation of the magnetization vector of the free layer to that of
the pinned layer. When the two magnetization vectors are parallel, the resistance
is the lowest; when the two magnetization vectors are antiparallel, the resistance
is the highest. The relative change of resistance is called the magnetoresistance
(MR) ratio. In certain embodiments, a spin valve element has a MR ratio of 1% to 20%,
such as 3% to 15 %, including 5% to 12%. In some cases, the MR ratio of a spin valve
element is 10% or more in a small magnetic field, e.g., 100 Oe. Changes in the resistance
of the spin valve element due to the presence of magnetic labels near the surface
of the spin valve element may be detected, as described above.
[0108] In certain embodiments, the signal from the spin valve element due to the magnetic
label depends on the distance between the magnetic label and the free layer of the
spin valve element. In some cases, the voltage signal from a magnetic label decreases
as the distance from the center of the magnetic label to the mid-plane of the free
layer increases. Thus, in certain instances, the free layer in the spin valve element
is positioned at the surface of the spin valve element. Positioning the free layer
at the surface of the spin valve element may minimize the distance between the free
layer and any bound magnetic labels, which may facilitate detection of the magnetic
labels.
[0109] In certain embodiments, the spin valve element may include a passivation layer disposed
on one or more of the spin valve element surfaces. In some cases, the passivation
layer has a thickness of 60 nm or less, such as 50 nm or less, including 40 nm or
less, 30 nm or less, 20 nm or less, 10 nm or less. For instance, the passivation layer
may have a thickness of 1 nm to 10 nm, such as from 1 nm to 5 nm, including from 1
nm to 3 nm. In certain embodiments, the passivation layer includes gold, tantalum,
SiO
2, Si
3N
4, combinations thereof, and the like.
Magnetic Tunnel Junction (MTJ) Magnetoresistive Elements
[0110] In certain embodiments, the magnetic sensor element is a magnetic tunnel junction
(MTJ) magnetoresistive element (also referred to herein as an MTJ element). In some
cases, the MTJ element includes a multilayer structure that includes a first ferromagnetic
layer, an insulating layer disposed on the first ferromagnetic layer, and a second
ferromagnetic layer disposed on the insulating layer. The insulating layer may be
a thin insulating tunnel barrier, and may include alumina, MgO, and the like. In some
cases, electron tunneling between the first and the second ferromagnetic layers depends
on the relative magnetization of the two ferromagnetic layers. For example, in certain
embodiments, the tunneling current is high when the magnetization vectors of the first
and second ferromagnetic layers are parallel and the tunneling current is low when
the magnetization vectors of the first and second ferromagnetic layers antiparallel.
[0111] In some instances, a MTJ element has a magnetoresistance ratio (MR) of 1% to 300%,
such as 10% to 250%, including 25% to 200%. Changes in the resistance of the MTJ element
due to the presence of magnetic labels near the surface of the MTJ element may be
detected, as described above. In some instances, the MTJ element has an MR of 50%
or more, or 75% or more, or 100% or more, or 125% or more, or 150% or more, or 175%
or more, or 200% or more, or 225% or more, or 250% or more, or 275% or more, or 200%
or more. For instance, the MTJ element may have an MR of 225% or more.
[0112] In certain embodiments, the second ferromagnetic layer (e.g., the layer of the MTJ
element positioned at the surface of the MTJ element) includes two of more layers.
For example, the second ferromagnetic layer may include a first layer, a second layer
disposed on the first layer, and a third layer disposed on the second layer. In some
cases, the first layer is a thin ferromagnetic layer (e.g., NiFe, CoFe, CoFeB, and
the like). The thin metallic layer may have a thickness of 6 nm or less, such as 5
nm or less, including 4 nm or less, 3 nm or less, 2 nm or less, or 1 nm or less, or
0.5 nm or less. The second layer may include a conductive metal, e.g., copper, aluminum,
palladium, a palladium alloy, a palladium oxide, platinum, a platinum alloy, a platinum
oxide, ruthenium, a ruthenium alloy, a ruthenium oxide, silver, a silver alloy, a
silver oxide, tin, a tin alloy, a tin oxide, titanium, a titanium alloy, a titanium
oxide, tantalum, a tantalum alloy, a tantalum oxide, combinations thereof, and the
like. The second layer may have a thickness of 2 nm or less, such as 0.5 nm or less,
including 0.4 nm or less, 0.3 nm or less, 0.2 nm or less, or 0.1 nm or less. The third
layer may include a ferromagnetic material such as, but not limited to, NiFe, CoFe,
CoFeB, and the like. The third layer may have a thickness of 6 nm or less, such as
5 nm or less, including 4 nm or less, 3 nm or less, 2 nm or less, or 1 nm or less,
or 0.5 nm or less.
[0113] In some cases, the MTJ element is configured such that the distance between an associated
magnetic label and the top surface of the free layer ranges from 5 nm to 1000 nm,
or 10 nm to 800 nm, such as from 20 nm to 600 nm, including from 40 nm to 400 nm,
such as from 60 nm to 300 nm, including from 80 nm to 250 nm.
[0114] The MTJ element may include a passivation layer disposed on one or more of the MTJ
element surfaces. In some instances, the passivation layer has a thickness of 60 nm
or less, such as 50 nm or less, including 40 nm or less, 30 nm or less, 20 nm or less,
10 nm or less. For example, the passivation layer may have a thickness of 1 nm to
50 nm, such as from 1 nm to 40 nm, including from 1 nm to 30 nm, or form 1 nm to 20
nm. In some instances, the passivation layer has a thickness of 30 nm. In some cases,
the passivation layer includes gold, tantalum, a tantalum alloy, a tantalum oxide,
aluminum, an aluminum alloy, an aluminum oxide, SiO
2, Si
3N
4, ZrO
2, combinations thereof, and the like. In certain embodiments, a passivation layer
with a thickness as described above facilitates a maximization in signal detected
from magnetic labels specifically bound to the sensor surface or the inter-element
area while minimizing the signal from magnetic labels that are not specifically bound.
[0115] In certain embodiments, a MTJ element has dimensions ranging from 1 µm x 1 µm to
200 µm x 200 µm, including dimensions of 1 µm x 200 µm or less, such as 200 µm x 1
µm or less, for instance 150 µm x 10 µm or less, or 120 µm x 5 µm or less, or 120
µm x 0.8 µm or less, or 0.8 µm x 120 µm or less, or 100 µm x 0.7 µm or less, or 100
µm x 0.6 µm or less, or 100 µm x 0.5 µm or less, or 10 µm x 0.6 µm or less, or 10
µm x 0.5 µm or less. In some instances, a MTJ element has dimensions of 120 µm x 0.8
µm or less, such as 2.0 µm x 0.8 µm.
Magnetic Sensing Areas
[0117] In certain embodiments, the magnetic sensor device may be configured to include one
or more magnetic sensing areas. A magnetic sensing area may correspond to the area
of the device where an array of magnetic sensors (e.g., an array of biosensors) is
positioned. For instance, the magnetic sensing area may be an area on the surface
of the device that is exposed to the sample during use, and which has an array of
magnetic sensors (e.g., an array of biosensors) as described above.
[0118] The magnetic sensing area may be configured to include a fluid reservoir. The fluid
reservoir may be any of a variety of configurations, where the fluid reservoir is
configured to hold a sample in contact with the magnetic sensor arrays. Accordingly,
configurations of the fluid reservoirs may include, but are not limited to: cylindrical
well configurations, square well configurations, rectangular well configurations,
round bottom well configurations, and the like. For instance, the fluid reservoirs
may include walls that separate one fluid reservoir from adjacent fluid reservoirs.
The walls may be substantially vertical with respect to the surface of the reservoir
plate. In some cases, the walls of each fluid reservoir define a volume of space that
may receive a volume of sample equal to or less than the volume of space defined by
the fluid reservoir.
[0119] In certain embodiments, a fluid reservoir has a volume of 10 mL or less, or 5mL or
less, or 3 mL or less, or 1 mL or less, such as 500 µL or less, including 100 µL or
less, for example 50 µL or less, or 25 µL or less, or 10 µL or less, which is sufficient
to contain a sample volume of an equal or lesser volume.
MAGNETIC SENSOR SYSTEMS
[0120] In certain embodiments, the systems include a magnetic sensor device, and a magnetic
field source. The magnetic sensor device includes a support having two or more arrays
of magnetic sensors (e.g., arrays of biosensors) positioned thereon. The system may
be configured to obtain signals from each array of magnetic sensors indicating whether
one or more analytes is present in each sample.
[0121] In certain embodiments, the system includes a magnetic field source. The magnetic
field source may be configured to apply a magnetic field to the magnetic sensor device
(e.g., the magnetic sensor arrays) sufficient to produce a DC and/or AC field in the
assay sensing area (e.g. in the area where the magnetic sensor arrays are positioned
during signal acquisition). In some instances, the magnetic field source is configured
to produce a magnetic field with a magnetic field strength of 1 Oe or more, or 5 Oe
or more, or 10 Oe or more, or 20 Oe or more, or 30 Oe or more, or 40 Oe or more, or
50 Oe or more, or 60 Oe or more, or 70 Oe or more, or 80 Oe or more, or 90 Oe or more,
or 100 Oe or more.
[0122] The magnetic field source may be positioned such that a magnetic field is produced
in the area where the magnetic sensor arrays are positioned when the magnetic sensor
device is in use. In some cases, the magnetic field source is configured to generate
a uniform, controllable magnetic field around the set of fluid reservoirs on the reservoir
plate where an assay is being performed. The magnetic field source may include one
or more, such as two or more, three or more, four or more magnetic field generating
components. In some cases, the magnetic field source may include one or more electromagnets,
such as coil electromagnets. The coil electromagnets may include wire-wound coils.
For example, the magnetic field source may include two electromagnets arranged in
a Helmholtz coil geometry.
[0123] Embodiments of the systems further include computer-based systems. The systems may
be configured to qualitatively and/or quantitatively assess binding interactions as
described above. A "computer-based system" refers to the hardware, software, and data
storage components used to analyze the signals from the magnetic sensors. The hardware
of the computer-based systems may include a central processing unit (CPU), inputs,
outputs, and data storage components. Any of a variety of computer-based systems is
suitable for use in the subject systems. The data storage components may include any
computer readable medium that includes a device for recording signals from the magnetic
sensor arrays, or an accessible memory component that can store signals from the magnetic
sensor arrays.
[0124] To "record" data, programming or other information on a computer readable medium
refers to a process for storing information, using any such methods as known in the
art. Any convenient data storage structure may be chosen, depending on the method
used to access the stored information. A variety of data processor programs and formats
can be used for storage, e.g. word processing text file, database format, etc.
[0125] In certain embodiments, the system includes an activation and signal processing unit.
The activation and signal processing unit may be configured to operably couple to
the magnetic sensor device. In some instances, the activation and signal processing
unit is electrically coupled to the magnetic sensor device. The activation and signal
processing unit may be electrically coupled such as to provide bi-directional communication
to and from the magnetic sensor device. For example, the activation and signal processing
unit may be configured to provide power, activation signals, etc. to components of
the magnetic sensor device, such as, but not limited to the magnetic sensor arrays.
As such, the activation and signal processing unit may include an activation signal
generator. The activation signal generator may be configured to provide power, activation
signals, etc. to components of the analyte detection device, such as, but not limited
to the magnetic sensor arrays. In some instances, the activation and signal processing
unit is configured to apply a voltage across the magnetic sensor arrays ranging from
1 mV to 10 V, such as 100 mV to 5 V, including 200 mV to 1 V, for example, 300 mV
to 500 mV. In some cases, the activation and signal processing unit is configured
to apply a voltage across the magnetic sensor arrays of 500 mV.
[0126] Additionally, the activation and signal processing unit may be configured to receive
signals from the magnetic sensor device, such as from the magnetic sensor arrays of
the magnetic sensor device. The signals from the magnetic sensor arrays of the magnetic
sensor device may be used to detect the presence of one or more analytes in the samples.
In some instances, the activation and signal processing unit may include a processor
configured to output an analyte detection result in response to receiving signals
from the magnetic sensor arrays. Thus, the processor of the activation and signal
processing unit may be configured to receive signals from the magnetic sensor device,
process the signals according to a predetermined algorithm, obtain a result related
to the presence of one or more analytes in the samples, and output the result to a
user in a human-readable or an audible format.
[0127] A "processor" references any hardware and/or software combination that will perform
one or more programmed functions. For example, any processor herein may be a programmable
digital microprocessor such as available in the form of an electronic controller,
mainframe, server or personal computer (e.g., desktop or portable). Where the processor
is programmable, suitable programming can be communicated from a remote location to
the processor, or previously saved in a computer program product (such as a portable
or fixed computer readable storage medium, whether magnetic, optical or solid-state
device based). For example, a magnetic medium, optical disk or solid-state memory
device may carry the programming, and can be read by a suitable reader communicating
with the processor.
[0128] In some instances, the subject systems are configured to modulate the current applied
to the magnetic sensor arrays (e.g., the sense current). The subject systems may also
be configured to modulate the magnetic field generated by the magnetic field source.
Modulating the sense current and the magnetic field may facilitate a minimization
in signal noise, and thus a maximization in the signal to noise ratio. Additional
aspects of modulating the sense current and the magnetic field are described in more
detail in
U.S. Application Publication No. 2011/0027901.
[0129] Embodiments of the subject systems may also include the following components: (a)
a wired or wireless communications module configured to transfer information between
the system and one or more users, e.g., via a user computer, as described below; and
(b) a processor for performing one or more tasks involved in the qualitative and/or
quantitative analysis of the signals from the magnetic sensors. In certain embodiments,
a computer program product is provided that includes a computer-usable medium having
control logic (e.g., a computer software program, including program code) stored therein.
The control logic, when executed by the processor of the computer, causes the processor
to perform functions described herein. In other embodiments, some functions are implemented
primarily in hardware using, for example, a hardware state machine. Implementation
of the hardware state machine so as to perform the functions described herein may
be accomplished using any convenient method and techniques.
[0130] In addition to the magnetic sensor device and activation and signal processing unit,
the systems may include a number of additional components, such as, but not limited
to: data output devices, e.g., monitors, speakers, etc.; data input devices, e.g.,
interface ports, buttons, switches, keyboards, etc.; fluid handling components, e.g.,
microfluidic components; power sources; power amplifiers; wired or wireless communication
components; etc. For example, the systems may include fluid handling components, such
as microfluidic fluid handling components. In certain embodiments, the microfluidic
fluid handling components are configured to deliver a fluid to the inter-element areas.
In some cases, the fluid includes one or more of the following: an assay composition,
a sample, a magnetic label, a capture probe, a reagent, and the like. In certain instances,
the microfluidic fluid handling components are configured to deliver small volumes
of fluid, such as 1 mL or less, such as 500 µL or less, including 100 µL or less,
for example 50 µL or less, or 25 µL or less, or 10 µL or less.
[0131] In certain embodiments, the system is a high-sensitivity analyte detector. By "high-sensitivity"
is meant that the system is configured to detect an analyte in a sample, where the
concentration of the analyte in the sample is low. In some cases, the system is configured
to produce a detectable signal indicating the presence of an analyte of interest in
a sample where the concentration of the analyte in the sample is 1 µM or less, such
as 100 nM or less, or 10 nM or less, or 1 nM or less, including 100 pM or less, or
10 pM or less, or 1 pM or less, for example 500 fM or less, or 250 fM or less, or
100 fM or less, or 50 fM or less, or 25 fM or less, such as 10 fM or less, or 5 fM
or less, or 1 fM or less. Stated another way, the system may be configured to have
a detection limit, e.g., a lower limit of quantitation (LLOQ), of 1 µM or less, such
as 100 nM or less, or 10 nM or less, or 1 nM or less, including 100 pM or less, or
10 pM or less, or 1 pM or less, for example 500 fM or less, or 250 fM or less, or
100 fM or less, or 50 fM or less, or 25 fM or less, such as 10 fM or less, or 5 fM
or less, or 1 fM or less.
[0132] In certain embodiments, the systems include a display. The display may be configured
to provide a visual indication of an analyte detection result obtained from the activation
and signal processing unit, as described above. The display may be configured to display
a qualitative analyte detection result. For instance, the qualitative display may
be configured to display qualitative indicators to a user that a sample includes or
does not include a specific analyte of interest. In some embodiments, the display
may be configured to display an analyte detection result, where the analyte detection
result is a quantitative result, e.g., a quantitative measurement of the concentration
of an analyte in a sample. For example, in embodiments where the system is configured
to output a quantitative analyte detection result, the system may include a display
configured to display the quantitative analyte detection result.
[0133] The magnetic sensor device optionally includes a programmable memory, which prior
to and during the use of the magnetic sensor device can be programmed with relevant
information such as: calibration data for each individual sensor; a record of how
the biochip has been prepared with surface functionalization molecules prior to the
assay; a record of all completed assay steps; a record about which sample was measured;
a record of the measurement results; and the like.
METHODS
[0134] Aspects of the present disclosure also include a method for evaluating whether an
analyte is present in a sample. The method includes contacting a magnetic sensor device
with a sample to generate a signal. In addition, the method includes evaluating whether
the analyte is present in each sample based on the signal.
[0135] Embodiments of the methods are directed to evaluating whether an analyte is present
in a sample, e.g., determining the presence or absence of one or more analytes in
a sample. In certain embodiments of the methods, the presence of one or more analytes
in the sample may be determined qualitatively or quantitatively. Qualitative determination
includes determinations in which a simple yes/no result with respect to the presence
of an analyte in the sample is provided to a user. Quantitative determination includes
both semi-quantitative determinations in which a rough scale result, e.g., low, medium,
high, is provided to a user regarding the amount of analyte in the sample and fine
scale results in which an exact measurement of the concentration of the analyte is
provided to the user.
[0136] In some embodiments, the methods include the uniplex analysis of an analyte in a
sample. By "uniplex analysis" is meant that a sample is analyzed to detect the presence
of one analyte in the sample. For example, a sample may include a mixture of an analyte
of interest and other molecular entities that are not of interest. In some cases,
the methods include the uniplex analysis of the sample to determine the presence of
the analyte of interest in the sample mixture.
[0137] Certain embodiments include the multiplex analysis of two or more analytes in a sample.
By "multiplex analysis" is meant that the presence of two or more distinct analytes,
in which the two or more analytes are different from each other, is determined. For
example, analytes may include detectable differences in their molecular structure,
sequence, and the like. In some instances, the number of analytes is greater than
2, such as 4 or more, 6 or more, 8 or more, etc., up to 20 or more, e.g., 50 or more,
including 100 or more, or 1000 or more distinct analytes. In certain embodiments,
the methods include the multiplex analysis of 2 to 1000 distinct analytes, such as
4 to 500 distinct analytes, including 4 to 200 distinct analytes, or 4 to 100 distinct
analytes, or 4 to 50 distinct analytes, or 4 to 20 distinct analytes. In certain embodiments,
several multiplex assays may be conducted in parallel substantially simultaneously.
[0138] In some instances, the methods are wash-free methods of evaluating the presence of
one or more analytes in a sample. By "wash-free" is meant that no washing step is
performed following reagent and/or sample contact with a magnetic sensor. As such,
no step is performed during the assays of these embodiments in which unbound reagent
(e.g., unbound magnetic labels) or unbound sample is removed from the magnetic sensor
surface. Accordingly, while the methods may include sequential contact of one or more
distinct reagents and/or samples to a magnetic sensor surface, at no point during
the assay is the sample surface contacted with a fluid in a manner that removes unbound
reagent or sample from the magnetic sensor surface. For example, in certain embodiments,
no washing step is performed following contact of the magnetic sensor surface with
a sample. In some cases, the method does not include a washing step following contact
of the magnetic sensor surface with a magnetic label. In certain instances, no washing
step is performed following contact of the magnetic sensor surface with a capture
probe.
[0139] In certain embodiments where a wash step is performed, the wash step does not substantially
change the signal from the magnetic sensor. The wash step may not result in a substantial
change in the signal from the magnetic sensor because, in some instances, unbound
magnetic labels do not have a substantially detectable signal as described herein.
For example, if a wash step is performed, in some cases, the wash step results in
a signal change of 25% or less, such as 20% or less, or 15% or less, or 10% or less
or 5% or less, or 4% or less, or 3% or less, or 2% or less, or 1% or less. In some
embodiments, the wash step results in a decrease in the signal from the magnetic sensor
of 25% or less, such as 20% or less, or 15% or less, or 10% or less or 5% or less,
or 4% or less, or 3% or less, or 2% or less, or 1% or less.
[0140] Aspects of the methods may also include obtaining a real-time signal from the magnetic
sensor device. As such, embodiments of the method include obtaining a real-time signal
from the magnetic sensor arrays. By "real-time" is meant that a signal is observed
as it is being produced or immediately thereafter. For example, a real-time signal
is obtained from the moment of its initiation and is obtained continuously over a
given period of time. Accordingly, certain embodiments include observing the evolution
in real time of the signal associated with the occurrence of a binding interaction
of interest (e.g., the binding of the analyte of interest to the magnetic sensor or
the inter-element area and/or binding of a magnetic label to the analyte of interest).
The real-time signal may include two or more data points obtained over a given period
of time, where in certain embodiments the signal obtained is a continuous set of data
points (e.g., in the form of a trace) obtained continuously over a given period of
time of interest. The time period of interest may vary, ranging in some instances
from 0.5 min to 60 min, such as 1 min to 30 min, including 1 min to 15 min, or 1 min
to 10 min. For example, the time period may begin at the moment of initiation of the
real-time signal and may continue until the magnetic sensor reaches a maximum or saturation
level (e.g., where all the analyte binding sites on the magnetic sensor are occupied).
For example, in some cases, the time period begins when a sample is contacted with
the magnetic sensor. In some cases, the time period may begin prior to contacting
the sample with the magnetic sensor, e.g., to record a baseline signal before contacting
sample to the magnetic sensor. The number of data points in the signal may also vary,
where in some instances, the number of data points is sufficient to provide a continuous
stretch of data over the time course of the real-time signal. By "continuous" is meant
that data points are obtained repeatedly with a repetition rate of 1 data point per
minute or more, such as 2 data points per minute or more, including 5 data points
per minute or more, or 10 data points per minute or more, or 30 data points per minute
or more, or 60 data points per minute or more (e.g., 1 data point per second or more),
or 2 data points per second or more, or 5 data points per second or more, or 10 data
points per second or more, or 20 data points per second or more, or 50 data points
per second or more, or 75 data points per second or more, or 100 data points per second
or more.
[0141] In certain embodiments, the real-time signal is a real-time analyte-specific signal.
A real-time analyte-specific signal is a real-time signal as described above that
is obtained only from the specific analyte of interest. In these embodiments, unbound
analytes and unbound magnetic labels do not produce a detectable signal. In these
embodiments, non-specifically bound analytes and non-specifically bound magnetic labels
do not produce a detectable signal. As such, the real-time signal that is obtained
is only from the specific magnetically-labeled analyte of interest bound to the magnetic
sensor or inter-element area and substantially no signal is obtained from unbound
or non-specifically bound magnetic labels or other reagents (e.g., analytes not specifically
bound to the sensor).
[0142] In some embodiments, the signal is observed while the assay device is in a wet condition.
By "wet" or "wet condition" is meant that the assay composition (e.g., an assay composition
that includes a sample, a magnetic label, and a capture probe) is still in contact
with the surface of the magnetic sensor. As such, there is no need to perform any
washing steps to remove the non-binding moieties that are not of interest or the excess
unbound magnetic labels or capture probes. In certain embodiments, the use of magnetic
labels and magnetic sensors, as described above, facilitates "wet" detection because
the signal induced in the magnetic sensor by the magnetic label decreases as the distance
between the magnetic label and the surface of the magnetic sensor increases. For example,
the use of magnetic labels and magnetic sensors, as described above, may facilitate
"wet" detection because the magnetic field generated by the magnetic labels decreases
as the distance between the magnetic label and the surface of the magnetic sensor
increases. In some instances, the magnetic field of the magnetic label bound to the
surface-bound analyte significantly exceeds the magnetic field from the unbound magnetic
labels dispersed in solution. For example, as described above, a real-time analyte-specific
signal may be obtained only from the specific magnetically-labeled analyte of interest
bound to the magnetic sensor and substantially no signal may be obtained from unbound
magnetic labels dispersed in solution (e.g., not specifically bound to the sensor).
The unbound magnetic labels dispersed in solution may be at a greater distance from
the surface of the magnetic sensor and may be in Brownian motion, which may reduce
the ability of the unbound magnetic labels to induce a detectable change in the resistance
of the magnetic sensor.
Assay Protocol
[0143] A typical assay protocol, as well as the individual components of the assay, is described
in the following sections. In certain embodiments, the method includes contacting
a magnetic sensor array with an assay composition that includes a sample. The magnetic
sensor array may then be contacted with a magnetic label and a capture probe configured
to bind to the magnetic label. A signal is obtained from the sensor to detect the
presence of the analyte in the sample. Each of these steps will now be described in
greater detail.
Sample
[0144] As described above, assay compositions that may be assayed in the subject methods
include a sample. Samples that may be assayed in the subject methods may vary, and
include both simple and complex samples. Simple samples are samples that include the
analyte of interest, and may or may not include one or more molecular entities that
are not of interest, where the number of these non-interest molecular entities may
be low, e.g., 10 or less, 5 or less, etc. Simple samples may include initial biological
or other samples that have been processed in some manner, e.g., to remove potentially
interfering molecular entities from the sample. By "complex sample" is meant a sample
that may or may not have the analytes of interest, but also includes many different
proteins and other molecules that are not of interest. In some instances, the complex
sample assayed in the subject methods is one that includes 10 or more, such as 20
or more, including 100 or more, e.g., 10
3 or more, 10
4 or more (such as 15,000; 20,000 or 25,000 or more) distinct (i.e., different) molecular
entities, that differ from each other in terms of molecular structure.
[0145] In certain embodiments, the samples of interest are biological samples, such as,
but not limited to, urine, blood, serum, plasma, saliva, perspiration, feces, cheek
swabs, cerebrospinal fluid, cell lysate samples, and the like. The sample can be a
biological sample or can be extracted from a biological sample derived from humans,
animals, plants, fungi, yeast, bacteria, tissue cultures, viral cultures, or combinations
thereof using conventional methods for the successful extraction of DNA, RNA, proteins
and peptides. In some instances, the samples of interest are water, food or soil samples.
[0146] As described above, the samples that may be assayed in the subject methods may include
one or more analytes of interest. Examples of detectable analytes include, but are
not limited to: nucleic acids, e.g., double or single-stranded DNA, double or single-stranded
RNA, DNA-RNA hybrids, DNA aptamers, RNA aptamers, etc.; proteins and peptides, with
or without modifications, e.g., antibodies, diabodies, Fab fragments, DNA or RNA binding
proteins, phosphorylated proteins (phosphoproteomics), peptide aptamers, epitopes,
and the like; small molecules such as inhibitors, activators, ligands, etc.; oligo
or polysaccharides; mixtures thereof; and the like.
Magnetic Labels
[0147] Assay compositions that may be assayed in the subject methods include a magnetic
label. Magnetic labels are labeling moieties that are detectable by a sensor, such
as a magnetic sensor, when the magnetic label is positioned near the magnetic sensor.
While the distance between the magnetic label and magnetic sensor during detection
may vary depending on the nature of the specific magnetic label and magnetic sensor,
in some instances this distance ranges from 1 nm to 1000 nm from the magnetic sensor,
or 1 nm to 800 nm from the magnetic sensor, such as from 5 nm to 500 nm, including
from 5 nm to 100 nm. In certain embodiments, the magnetic labels are detectable labels
that are configured to specifically bind to an analyte of interest. The terms "specific
binding," "specifically bind," and the like, refer to the ability of a first binding
molecule or moiety (e.g., a target-specific binding moiety) to preferentially bind
directly to a second binding molecule or moiety (e.g., a target molecule) relative
to other molecules or moieties in a solution or assay mixture. In certain embodiments,
the affinity between a first binding molecule or moiety and a second binding molecule
or moiety when they are specifically bound to each other in a binding complex is characterized
by a K
D (dissociation constant) of less than 10
-6 M, less than 10
-7 M, less than 10
-8 M, less than 10
-9 M, less than 10
-10 M, less than 10
-11 M, less than 10
-12 M, less than 10
-13 M, less than 10
-14 M, or less than 10
-15 M.
[0148] Binding of the magnetic label to the analyte of interest allows the analyte of interest
to be detected by a magnetic sensor when the analyte of interest, and thus the bound
magnetic label, is positioned near the magnetic sensor. In some cases, the magnetic
labels are configured to bind directly to an analyte of interest. In other cases,
the magnetic labels are configured to indirectly bind to an analyte of interest. For
instance, a magnetic label may be configured to specifically bind to a capture probe,
and the capture probe may be configured to specifically bind to the analyte of interest.
Thus, binding of the magnetic label and the analyte of interest to the capture probe
indirectly binds the magnetic label to the analyte of interest, e.g., to produce a
labeled analyte. In some instances, the binding of the magnetic label and analyte
to the capture probe is simultaneous.
[0149] In certain embodiments, the magnetic label is functionalized with one member of a
binding pair. By "binding pair" or "specific binding pair" is meant two complementary
binding molecules or moieties that specifically bind to each other in a binding complex.
For example, a magnetic label may be functionalized with a first member of a binding
pair and an analyte of interest may be functionalized with a second member of a binding
pair. Thus, contacting the first and second members of the binding pair may form a
binding complex between the magnetic label and the analyte of interest. In other cases,
a magnetic label is functionalized with a first member of a binding pair and a capture
probe is functionalized with a second member of a binding pair. Thus, contacting the
first and second members of the binding pair may form a binding complex between the
magnetic label and the capture probe. As described above, in some cases, the capture
probe is configured to specifically bind to an analyte of interest. As such, the magnetic
label may be indirectly bound to the analyte of interest through the binding complex
formed between the magnetic label and the capture probe. Suitable specific binding
pairs include, but are not limited to: a member of a receptor/ligand pair; a ligand-binding
portion of a receptor; a member of an antibody/antigen pair; an antigen-binding fragment
of an antibody; a hapten; a member of a lectin/carbohydrate pair; a member of an enzyme/substrate
pair; biotin/avidin; biotin/streptavidin; digoxin/antidigoxin; and the like.
[0150] In certain embodiments, the magnetic label is functionalized with streptavidin and
the capture probe is functionalized with biotin. As such, the magnetic label may specifically
bind to the capture probe through the specific binding interaction between streptavidin
and biotin. Other types of binding interactions are also possible. For example, the
magnetic label may be functionalized with biotin and the capture probe may be functionalized
with streptavidin. Alternatively, the magnetic label and the capture probe may be
functionalized with complementary members of other specific binding pairs, as described
above.
[0151] In some instances, the magnetic label is stably associated with one member of a binding
pair. By "stably associated" is meant that the magnetic label and the member of the
binding pair maintain their position relative to each other in space under the conditions
of use, e.g., under the assay conditions. As such, the magnetic label and the member
of the binding pair can be non-covalently or covalently stably associated with each
other. Examples of non-covalent association include non-specific adsorption, binding
based on electrostatic (e.g., ion-ion pair interactions), hydrophobic interactions,
hydrogen bonding interactions, and the like. Examples of covalent binding include
covalent bonds formed between the member of the binding pair and a functional group
present on the surface of the magnetic label.
[0152] In certain embodiments, the magnetic labels are colloidal. The terms "colloid" or
"colloidal" refer to a mixture in which one substance is dispersed throughout another
substance. Colloids include two phases, a dispersed phase and a continuous phase.
In some instances, colloidal magnetic labels remain dispersed in solution and do not
precipitate or settle out of solution. Colloidal magnetic labels that remain dispersed
in solution may facilitate a minimization in background signals and non-specific interaction
of the magnetic labels with the magnetic sensor or inter-element area. For example,
the methods may include contacting a magnetic sensor with an assay composition that
includes a sample and a magnetic label, such that an analyte of interest in the sample
is bound to the surface of the magnetic sensor or inter-element area. Because the
colloidal magnetic labels remain dispersed in solution, the magnetic labels are not
positioned near enough to the magnetic sensor to induce a detectable signal in the
magnetic sensor, which facilitates a minimization in background signals. In some cases,
specific binding of the magnetic labels to the surface-bound analyte positions the
magnetic label near the magnetic sensor, such that a detectable signal is induced
in the magnetic sensor.
[0153] Magnetic labels that may be employed in various methods (e.g., as described herein)
may vary, and include any type of label that induces a detectable signal in a magnetic
sensor when the magnetic label is positioned near the surface of the magnetic sensor.
For example, magnetic labels may include, but are not limited to, magnetic labels,
optical labels (e.g., surface enhanced Raman scattering (SERS) labels), fluorescent
labels, and the like. Each of these types of magnetic labels is discussed in more
detail below.
[0154] Magnetic labels are labeling moieties that, when sufficiently associated with a magnetic
sensor or inter-element area, are detectable by the magnetic sensor and cause the
magnetic sensor to output a signal. For example, the presence of a magnetic label
near the magnetic sensor may induce a detectable change in the magnetic sensor, such
as, but not limited to, a change in resistance, conductance, inductance, impedance,
etc. In some cases, the presence of a magnetic label near the magnetic sensor induces
a detectable change in the resistance of the magnetic sensor. Magnetic labels of interest
may be sufficiently associated with a magnetic sensor if the distance between the
center of the magnetic label and the magnetic sensor is 1000 nm or less, such as 800
nm or less, such as 400 nm or less, including 100 nm or less.
[0155] In certain instances, the magnetic labels include one or more materials selected
from paramagnetic, superparamagnetic, ferromagnetic, ferromagnetic, antiferromagnetic
materials, combinations thereof, and the like. For example, the magnetic labels may
include superparamagnetic materials. In certain embodiments, the magnetic labels are
configured to be nonmagnetic in the absence of an external magnetic field. By "nonmagnetic"
is meant that the magnetization of a magnetic labels is zero or averages to zero over
a certain period of time. In some cases, the magnetic label may be nonmagnetic due
to random flipping of the magnetization of the magnetic label over time. Magnetic
labels that are configured to be nonmagnetic in the absence of an external magnetic
field may facilitate the dispersion of the magnetic labels in solution because nonmagnetic
labels do not normally agglomerate in the absence of an external magnetic field or
even in the presence of a small magnetic field in which thermal energy is still dominant.
In certain embodiments, the magnetic labels include superparamagnetic materials or
synthetic antiferromagnetic materials. For instance, the magnetic labels may include
two or more layers of antiferromagnetically-coupled ferromagnets.
[0156] In certain embodiments, the magnetic labels are high moment magnetic labels. The
magnetic moment of a magnetic label is a measure of its tendency to align with an
external magnetic field. By "high moment" is meant that the magnetic labels have a
greater tendency to align with an external magnetic field. Magnetic labels with a
high magnetic moment may facilitate the detection of the presence of the magnetic
labels near the surface of the magnetic sensor because it is easier to induce the
magnetization of the magnetic labels with an external magnetic field.
[0157] In certain embodiments, the magnetic labels include, but are not limited to, Co,
Co alloys, ferrites, cobalt nitride, cobalt oxide, Co-Pd, Co-Pt, iron, iron oxides,
iron alloys, Fe-Au, Fe-Cr, Fe-N, Fe
3O
4, Fe-Pd, Fe-Pt, Fe-Zr-Nb-B, Mn-N, Nd-Fe-B, Nd- Fe-B-Nb-Cu, Ni, Ni alloys, combinations
thereof, and the like. Examples of high moment magnetic labels include, but are not
limited to, Co, Fe or CoFe nanocrystals, which may be superparamagnetic at room temperature,
and synthetic antiferromagnetic nanoparticles.
[0158] In some embodiments, the surface of the magnetic label is modified. In certain instances,
the magnetic labels may be coated with a layer configured to facilitate stable association
of the magnetic label with one member of a binding pair, as described above. For example,
the magnetic label may be coated with a layer of gold, a layer of poly-L-lysine modified
glass, dextran, and the like. In certain embodiments, the magnetic labels include
one or more iron oxide cores imbedded in a dextran polymer. Additionally, the surface
of the magnetic label may be modified with one or more surfactants. In some cases,
the surfactants facilitate an increase in the water solubility of the magnetic labels.
In certain embodiments, the surface of the magnetic labels is modified with a passivation
layer. The passivation layer may facilitate the chemical stability of the magnetic
labels in the assay conditions. For example, the magnetic labels may be coated with
a passivation layer that includes gold, iron oxide, polymers (e.g., polymethylmethacrylate
films), and the like.
[0159] In certain embodiments, the magnetic labels have a spherical shape. Alternatively,
the magnetic labels can be disks, rods, coils, or fibers. In some cases, the size
of the magnetic labels is such that the magnetic labels do not interfere with the
binding interaction of interest. For example, the magnetic labels may be comparable
to the size of the analyte and the capture probe, such that the magnetic labels do
not interfere with the binding of the capture probe to the analyte. In some cases,
the magnetic labels are magnetic nanoparticles, or contain multiple magnetic nanoparticles
held together by a suitable binding agent. In some embodiments, the average diameter
of the magnetic labels is from 5 nm to 250 nm, such as from 5 nm to 150 nm, including
from 10 nm to 100 nm, for example from 25 nm to 75 nm. For example, magnetic labels
having an average diameter of 5 nm, 10 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm,
50 nm, 55 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm, as well as magnetic labels having
average diameters in ranges between any two of these values, may be used with the
subject methods. In some instances, the magnetic labels have an average diameter of
50 nm.
Assay Composition Production
[0161] In some instances, the method includes producing the assay composition by sequentially
contacting the magnetic sensor array (e.g., array of biosensors) with the sample and
the magnetic label. For example, the method may include contacting the magnetic sensor
array first with the sample and subsequently with the magnetic label. Alternatively,
the method may include contacting the magnetic sensor array first with the magnetic
label and subsequently with the sample.
[0162] In other embodiments, the method includes combining the sample and the magnetic label
to produce the assay composition and then contacting the magnetic sensor array with
the assay composition. For instance, the method may include first combining the sample
and the magnetic label to produce the assay composition. Then the magnetic sensor
may be contacted with the assay composition, as described above. Subsequently, the
method may include contacting the magnetic sensor with the capture probe, as described
in detail below.
Capture Probe
[0163] A capture probe can be any molecule that specifically binds to a protein or nucleic
acid sequence that is being targeted (e.g., the analyte of interest). Depending on
the nature of the analyte, capture probes can be, but are not limited to, (a) single
strands of DNA complementary to a unique region of the target DNA or RNA sequence
for the detection of nucleic acids; (b) antibodies against an epitope of the peptidic
analyte for the detection of proteins and peptides; (c) any recognition molecule,
such as a member of a specific binding pair. For example, suitable specific binding
pairs include, but are not limited to: a member of a receptor/ligand pair; a ligand-binding
portion of a receptor; a member of an antibody/antigen pair; an antigen-binding fragment
of an antibody; a hapten; a member of a lectin/carbohydrate pair; a member of an enzyme/substrate
pair; biotin/avidin; biotin/streptavidin; digoxin/antidigoxin; and the like.
[0164] In certain embodiments, the capture probe includes an antibody. The capture probe
antibody may specifically bind to an analyte of interest. In some cases, the capture
probe is a modified antibody. The modified antibody may be configured to specifically
bind to the analyte of interest and may also include one or more additional members
of a specific binding pair. The one or more members of a specific binding pair may
be configured to specifically bind to a complementary member of the specific binding
pair. In certain instances, the complementary member of the specific binding pair
is bound to the magnetic label, as described above. For example, the capture probe
may be an antibody that specifically binds to an analyte of interest. In addition,
the capture probe may be modified to include biotin. As described above, in certain
embodiments, magnetic labels may be modified to include streptavidin. As such, the
capture probe may be configured to specifically bind to the analyte of interest (e.g.,
through an antibody-antigen interaction) and to specifically bind to the magnetic
label (e.g., through a streptavidin-biotin interaction). In some cases, the capture
probe is configured to bind to the analyte of interest and the magnetic label. Stated
another way, the capture probe may be configured such that specific binding of the
analyte to the capture probe does not significantly interfere with the ability of
the capture probe to specifically bind to the magnetic label. Similarly, the capture
probe may be configured such that specific binding of the magnetic label to the capture
probe does not significantly interfere with the ability of the capture probe to specifically
bind to the analyte.
[0165] In certain embodiments, the capture probe specifically binds to an analyte of interest.
In some cases, the capture probe can be identified so that the presence of the analyte
of interest can then be detected. Capture probes may be identified by any of the methods
described herein. For example, as described above, analytes may be directly or indirectly
bound to a magnetic sensor or inter-element area. The capture probe may contact and
specifically bind to the analyte of interest. As indicated above, the capture probe
may be configured to bind to a magnetic label and the analyte of interest. In certain
instances, simultaneous binding of the capture probe to surface-bound analyte and
the magnetic label positions the magnetic label within the detection range of the
magnetic sensor, such that a detectable signal is induced in the magnetic sensor.
[0166] In some cases, false-positive signals due to non-specific binding of the capture
probe to moieties not of interest are minimized. For example, non-specific binding
of the capture probe to other moieties not of interest, which are not bound to the
surface of the magnetic sensor array and remain in solution, will not induce a detectable
or non-negligible signal in the magnetic sensor because the magnetic label bound to
the capture probe will not be positioned within the detection range of the magnetic
sensor.
[0167] As described above, the magnetic label may be colloidal, such that the magnetic label
remains dispersed in the assay composition solution. In certain instances, the kinetics
of the capture probe diffusion to the surface of the magnetic sensor and binding to
the analyte is significantly faster than the kinetics of the diffusion of the magnetic
labels to the surface of the magnetic sensor. Having faster kinetics for the binding
of the capture probe to the analyte than the diffusion of the magnetic label to the
surface of the magnetic sensor array may facilitate a minimization in false positive
signals due to non-specific positioning of the magnetic label within the detection
range of the magnetic sensor.
[0168] In certain embodiments, the magnetic sensor arrays are contacted with the capture
probe after the magnetic sensor arrays are contacted with the assay composition. Thus,
the methods may include first producing an assay composition that includes a sample
and a magnetic label. The magnetic sensor array may then be contacted with the assay
composition. Subsequently, the magnetic sensor array may be contacted with a capture
probe.
[0169] Other methods are also possible. For example, the method may include first contacting
the magnetic sensor arrays to the capture probe, and subsequently contacting the magnetic
sensor arrays to the assay composition, where the assay composition includes a sample
and a magnetic label. In both of the methods described above, the magnetic label is
present in the assay composition prior to contacting the magnetic sensor array to
the capture probe.
[0170] As described above, in some instances, the methods are wash-free methods of evaluating
the presence of one or more analytes in a sample. As such, in certain embodiments,
contacting the magnetic sensor arrays with assay components does not include any washing
steps before or after contacting the magnetic sensor arrays with each component of
the assay composition. Thus, no washing step is performed either before or after the
magnetic sensor is contacted with any of the assay components.
Obtaining a Signal to Determine Whether an Analyte Is Present in a Sample
[0171] Embodiments of the subject methods also include obtaining a signal from a magnetic
sensor to detect the presence of an analyte in a sample. As described above, a magnetic
label may be bound, either directly or indirectly, to the analyte, which in turn may
be bound, either directly or indirectly, to the magnetic sensor. If the bound magnetic
label is positioned within the detection range of the magnetic sensor, then the magnetic
sensor may provide a signal indicating the presence of the bound magnetic label, and
thus indicating the presence of the analyte.
[0172] Magnetic sensors may be configured to generate an electrical signal in response to
a magnetic label in proximity to the magnetic sensor. For example, a change in the
resistance of the magnetic sensor may be induced by changes in the local magnetic
field. In some cases, binding of a magnetic label (e.g., a magnetic label) in close
proximity to the magnetic sensor induces a detectable change in the local magnetic
field of the magnetic sensor. For example, the magnetic field created by the magnetic
labels that are bound to the analytes of interest may exceed the magnetic field that
is created by unbound magnetic labels that remain dispersed in the sample. Changes
in the local magnetic field of the magnetic sensor may be detected as a change in
the resistance of the magnetic sensor. In certain embodiments, unbound magnetic labels
do not produce a detectable signal in the magnetic sensor.
UTILITY
[0173] The subject systems and methods find use in a variety of different applications where
determination of the presence or absence, and/or quantification of one or more analytes
in a sample is desired. The subject systems and methods also find use in applications
where the screening of a plurality of samples is desired. In certain embodiments,
the methods are directed to detection of a set of biomarkers, e.g., two or more distinct
protein biomarkers, in a plurality of samples. For example, the methods may be used
in the rapid detection of two or more disease biomarkers in a group of serum samples,
e.g., as may be employed in the diagnosis of a disease condition in a subject, in
the ongoing management or treatment of a disease condition in a subject, etc.
[0174] In certain embodiments, the subject systems and methods find use in detecting biomarkers.
In some cases, the subject systems and methods may be used to detect the presence
or absence of particular biomarkers, as well as an increase or decrease in the concentration
of particular biomarkers in blood, plasma, serum, or other bodily fluids or excretions,
such as but not limited to saliva, urine, cerebrospinal fluid, lacrimal fluid, perspiration,
gastrointestinal fluid, amniotic fluid, mucosal fluid, pleural fluid, sebaceous oil,
exhaled breath, and the like.
[0175] The presence or absence of a biomarker or significant changes in the concentration
of a biomarker can be used to diagnose disease risk, presence of disease in an individual,
or to tailor treatments for the disease in an individual. For example, the presence
of a particular biomarker or panel of biomarkers may influence the choices of drug
treatment or administration regimes given to an individual. In evaluating potential
drug therapies, a biomarker may be used as a surrogate for a natural endpoint such
as survival or irreversible morbidity. If a treatment alters the biomarker, which
has a direct connection to improved health, the biomarker can serve as a surrogate
endpoint for evaluating the clinical benefit of a particular treatment or administration
regime. Thus, personalized diagnosis and treatment based on the particular biomarkers
or panel of biomarkers detected in an individual are facilitated by the subject methods
and systems. Furthermore, the early detection of biomarkers associated with diseases
is facilitated by the picomolar and/or femtomolar sensitivity of the subject methods
and systems. Due to the capability of detecting multiple biomarkers on a single magnetic
sensor device, the presently disclosed assay systems and methods finds use in screening
of a plurality of samples in multiplexed molecular diagnostics.
[0176] In certain embodiments, the subject systems and methods find use in detecting biomarkers
for a disease or disease state. In some cases, the disease is a cellular proliferative
disease, such as but not limited to, a cancer, a tumor, a papilloma, a sarcoma, or
a carcinoma, and the like. Thus, the subject systems and methods find use in detecting
the presence of a disease, such as a cellular proliferative disease, such as a cancer,
tumor, papilloma, sarcoma, carcinoma, or the like. In certain embodiments, the subject
systems and methods find use in detecting biomarkers for an infectious disease or
disease state. In some cases, the biomarkers can be molecular biomarkers, such as
but not limited to proteins, nucleic acids, carbohydrates, small molecules, and the
like. Similarly, the subject methods, systems and kits can be used to detect cardiovascular
diseases, central nervous diseases, kidney failures, diabetes, autoimmune diseases,
and many other diseases.
[0177] For example, in certain embodiments, the subject systems and methods find use in
detecting biomarkers, such as carcinoembryonic antigen (cancer embryonic antigen;
CEA). CEA refers to a set of highly related glycoproteins involved in cell adhesion,
which is normally produced in gastrointestinal tissue during fetal development, but
the production stops before birth. Therefore, CEA is usually present only at very
low levels in the blood of healthy adults. However, the serum levels of CEA may be
elevated in some types of cancer, and thus can be used as a tumor biomarker in clinical
assays.
[0178] In certain embodiments, the subject methods, systems and kits can be used to detect
the presence or absence, and/or quantification of one or more analytes in a plurality
of samples for food and/or environmental safety. For example, the subject systems
and methods can be used to determine the presence of analytes in a plurality of samples
of potentially contaminated water, soil or food, such as for the detection of infectious
disease agents, e.g., bacteria, viruses, molds, etc., including potential biological
warfare agents.
COMPUTER RELATED ASPECTS
[0179] A variety of computer-related aspects are also provided. Specifically, the data analysis
methods described in the previous sections may be performed using a computer. Accordingly,
provided is a computer-based system for analyzing data produced using the above methods
in order to provide qualitative and/or quantitative determination of a binding interaction
of interest.
[0180] In certain cases, the methods are coded onto a computer-readable medium in the form
of "programming", where the term "computer readable medium" as used herein refers
to any storage or transmission medium that participates in providing instructions
and/or data to a computer for execution and/or processing. Examples of storage media
include floppy disks, magnetic tape, CD-ROM, DVD-ROM, BD-ROM, a hard disk drive, a
ROM or integrated circuit, a magneto-optical disk, a solid-state memory device, a
computer readable card such as a PCMCIA card, and the like, whether or not such devices
are internal or external to the computer. A file containing information may be "stored"
on computer readable medium, where "storing" means recording information such that
it is accessible and retrievable at a later date by a computer. Examples of media
include, but are not limited to, non-transitory media, e.g., physical media in which
the programming is associated with, such as recorded onto, a physical structure. Non-transitory
media does not include electronic signals in transit via a wireless protocol.
[0181] In certain cases, computer programming may include instructions for directing a computer
to perform one or more assay steps to determine the presence of an analyte of interest
in a sample. For example, the computer programming may include instructions for directing
a computer to determine whether an analyte is present in a sample, e.g., determining
the presence or absence of one or more analytes in a sample. In certain cases, the
computer programming includes instructions for directing a computer to determine the
presence of one or more analytes in the sample qualitatively and/or quantitatively.
As described above, qualitative determination includes determinations in which a simple
yes/no result with respect to the presence of an analyte in the sample is provided
to a user. Quantitative determination includes both semi-quantitative determinations
in which a rough scale result, e.g., low, medium, high, is provided to a user regarding
the amount of analyte in the sample and fine scale results in which an exact measurement
of the concentration of the analyte is provided to the user.
[0182] In some cases, the computer programming includes instructions for directing a computer
to perform a uniplex analysis of an analyte in a sample. By "uniplex analysis" is
meant that a sample is analyzed to detect the presence of one analyte in the sample.
For example, a sample may include a mixture of an analyte of interest and other molecular
entities that are not of interest. In some cases, the computer programming includes
instructions for directing a computer to perform a uniplex analysis of the sample
to determine the presence of the analyte of interest in the sample mixture.
[0183] In certain cases, the computer programming includes instructions for directing a
computer to perform a multiplex analysis of two or more analytes in a sample. By "multiplex
analysis" is meant that the presence of two or more distinct analytes, in which the
two or more analytes are different from each other, is determined. For example, analytes
may include detectable differences in their molecular structure, sequence, and the
like, as described above. In some instances, the number of analytes is greater than
2, such as 4 or more, 6 or more, 8 or more, etc., up to 20 or more, e.g., 50 or more,
including 100 or more, or 1000 or more distinct analytes. In certain cases, the computer
programming includes instructions for directing a computer to perform a multiplex
analysis of 2 to 1000 distinct analytes, such as 4 to 500 distinct analytes, including
4 to 200 distinct analytes, or 4 to 100 distinct analytes, or 4 to 50 distinct analytes,
or 4 to 20 distinct analytes. In certain embodiments, the computer programming includes
instructions for directing a computer to perform several multiplex assays in parallel
substantially simultaneously.
[0184] With respect to computer readable media, "permanent memory" refers to memory that
is permanent. Permanent memory is not erased by termination of the electrical supply
to a computer or processor. Computer hard-drive, CD-ROM, DVD-ROM, BD-ROM, solid state
memory and floppy disk are all examples of permanent memory. Random Access Memory
(RAM) is an example of non-permanent memory. A file in permanent memory may be editable
and re-writable.
KITS
[0185] Also provided are kits for practicing one or more embodiments of the above-described
methods. The subject kits may vary, and may include various devices and reagents.
Reagents and devices include those mentioned herein with respect to magnetic sensor
devices or components thereof (such as a magnetic sensor array), magnetic labels,
capture probes, analyte-specific probes, buffers, etc. The reagents, magnetic labels,
capture probes, etc. may be provided in separate containers, such that the reagents,
magnetic labels, capture probes, etc. may be used individually as desired. Alternatively,
one or more reagents, magnetic labels, capture probes, etc. may be provided in the
same container such that the one or more reagents, magnetic labels, capture probes,
etc. is provided to a user pre-combined.
[0186] In certain embodiments, the kits include a magnetic sensor device as described above,
and a magnetic label. For example, the magnetic label may be a magnetic nanoparticle,
as described above.
[0187] In some instances, the kits include at least reagents finding use in the methods
(e.g., as described above); and a computer readable medium having a computer program
stored thereon, wherein the computer program, when loaded into a computer, operates
the computer to qualitatively and/or quantitatively determine a binding interaction
of interest from a real-time signal obtained from a magnetic sensor; and a physical
substrate having an address from which to obtain the computer program.
[0188] In addition to the above components, the subject kits may further include instructions
for practicing the subject methods. These instructions may be present in the subject
kits in a variety of forms, one or more of which may be present in the kit. One form
in which these instructions may be present is as printed information on a suitable
medium or substrate, e.g., a piece or pieces of paper on which the information is
printed, in the packaging of the kit, in a package insert, etc. Yet another means
would be a computer readable medium, e.g., CD, DVD, Bluray, computer readable memory
device (e.g., a flash memory drive), etc., on which the information has been recorded.
Yet another means that may be present is a website address which may be used via the
Internet to access the information at a removed site. Any convenient means may be
present in the kits.
[0189] Although the foregoing embodiments has been described in some detail by way of illustration
and example for purposes of clarity of understanding, it is readily apparent to those
of ordinary skill in the art in light of the teachings of this present disclosure
that certain changes and modifications may be made thereto without departing from
scope of the appended claims.
[0190] The scope of the present disclosure, therefore, is not intended to be limited to
the exemplary embodiments shown and described herein. Rather, the scope of the present
disclosure is embodied by the appended claims.